U.S. patent application number 14/738371 was filed with the patent office on 2015-10-01 for particle detectors.
The applicant listed for this patent is Xtralis Technologies Ltd. Invention is credited to Kemal Ajay, Karl Boettger, Ron Knox.
Application Number | 20150276593 14/738371 |
Document ID | / |
Family ID | 43031595 |
Filed Date | 2015-10-01 |
United States Patent
Application |
20150276593 |
Kind Code |
A1 |
Knox; Ron ; et al. |
October 1, 2015 |
PARTICLE DETECTORS
Abstract
A beam detector including a light source, a receiver, and a
target, acting in cooperation to detect particles in a monitored
area. The target reflects incident light, resulting in reflected
light being returned to receiver. The receiver is capable of
recording and reporting light intensity at a plurality of points
across its field of view. In the preferred form the detector emits
a first light beam in a first wavelength band; a second light beam
in a second wavelength band; and a third light beam in a third
wavelength band, wherein the first and second wavelengths bands are
substantially equal and are different to the third wavelength
band.
Inventors: |
Knox; Ron; (Victoria,
AU) ; Boettger; Karl; (Mount Waverly, AU) ;
Ajay; Kemal; (Mount Waverly, AU) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Xtralis Technologies Ltd |
Nassau |
|
BS |
|
|
Family ID: |
43031595 |
Appl. No.: |
14/738371 |
Filed: |
June 12, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14451330 |
Aug 4, 2014 |
9057485 |
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14738371 |
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13318309 |
Feb 15, 2012 |
8797531 |
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PCT/AU2010/000511 |
May 3, 2010 |
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14451330 |
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Current U.S.
Class: |
356/338 |
Current CPC
Class: |
G01N 15/1434 20130101;
H01L 29/872 20130101; G01N 2201/0633 20130101; G08B 17/107
20130101; H01L 29/045 20130101; H01L 29/7786 20130101; G01N 21/53
20130101; H01L 29/1066 20130101; G01N 15/1459 20130101; G01N 21/538
20130101; G01N 15/0205 20130101; H01L 29/1037 20130101; H01L
29/1029 20130101; H01L 29/0657 20130101; G01N 15/10 20130101; G01N
2201/0627 20130101; G01N 2201/062 20130101; H01L 29/2003 20130101;
H01L 29/42356 20130101; G01N 2201/0621 20130101; G01N 2201/0696
20130101; G01N 2201/061 20130101 |
International
Class: |
G01N 21/53 20060101
G01N021/53; G01N 15/14 20060101 G01N015/14 |
Foreign Application Data
Date |
Code |
Application Number |
May 1, 2009 |
AU |
2009901922 |
May 1, 2009 |
AU |
2009901923 |
May 1, 2009 |
AU |
2009901924 |
May 1, 2009 |
AU |
2009901925 |
May 1, 2009 |
AU |
2009901926 |
May 1, 2009 |
AU |
2009901927 |
Claims
1. A method performed by a beam detector system configured to
detect particles in a monitored space, the method including:
generating with a light source at least one light beam having
components in at least a first wavelength band and a second
wavelength band such that the first wavelength band has a spatial
intensity light profile across the width of the beam that is
different to the spatial intensity profile in the second wavelength
band; receiving the at least one light source at an image sensor
after the at least one beam traverses the monitored space;
generating output signals representing a level of received light at
each of the first and second wavelengths from a region or regions
within a field of view of the image sensor that include the light
source; receiving the output signals and determining at least
partly on the basis of a relative reduction in the received light
in the second wavelength band compared to the first wavelength
band, from within the region or regions, that particles are
impinging on the at least one beam; wherein the spatial intensity
profiles for the components of the beam in the first wavelength
band and the second wavelength band are such that, in the event the
light source moves out of alignment with the sensor, the level of
light from the region or regions that is received by the image
sensor in the first wavelength band decreases before the level of
light received by the image sensor in the second wavelength band,
thereby causing a relative change in received light level that is
distinguishable from said relative reduction in the received light
intensity in the second wavelength band compare to the first
wavelength band caused by particles in the monitored space
impinging on the at least one beam.
2. The method of claim 1 wherein the beam width of light in the
first wavelength band is narrower than the beam width of light in
the second wavelength band.
3. The method of claim 1 wherein light in a first wavelength band
is at a longer wavelength than the second wavelength band.
4. The method of claim 1 wherein the light source includes a
plurality of light emitters, each emitter being configured to emit
light in one of the first and second wavelength bands.
5. The method of claim 4 wherein the plurality of light emitters
includes a light emitter corresponding to one of the first or
second wavelength bands arranged to surround one or more light
emitters corresponding to the other of the first or second
wavelength bands.
6. The method of claim 4 wherein plurality of light emitters
comprise a plurality of semiconductor dies in a common light
emitting diode (LED) package.
7. The method of claim 1 which includes a plurality of light
sources arranged with respect to the image sensor, such that at
least one beam from each light source is received at the image
sensor after the at least one beam traverses the monitored
space.
8. The method of claim 1 wherein the beam detector system is
arranged to detect smoke.
Description
PRIORITY CLAIM TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. Ser. No.
14/451,330, filed Aug. 4, 2014, which is a divisional application
of U.S. Ser. No. 13/318,309, filed Oct. 31, 2011, issued as U.S.
Pat. No. 8,797,531, which is a U.S. national stage application
filed under 35 U.S.C. .sctn.371 from International Application No.
PCT/AU2010/000511, filed May 3, 2010, and published as WO
2010/124347 A1 on Nov. 4, 2010, which claims priority to Australian
Application No. 2009901922, filed May 1, 2009, Australian
Application No. 2009901923, filed May 1, 2009, Australian
Application No. 2009901924, filed May 1, 2009, Australian
Application No. 2009901925, filed May 1, 2009, Australian
Application No. 2009901926, filed May 1, 2009, and Australian
Application No. 2009901927, filed May 1, 2009, which applications
and publication are incorporated by reference as if reproduced
herein and made a part hereof in their entirety, and the benefit of
priority of each of which is claimed herein.
FIELD OF THE INVENTION
[0002] The present invention relates to aspects of particle
detectors. By way of example the embodiments will be described in
relation to beam detectors adapted for detecting smoke. In one
aspect the present invention relates more generally to battery
powered devices, although the illustrative embodiment will be
described in connection with beam detectors.
BACKGROUND OF THE INVENTION
[0003] Various methods of detecting particles in air are known. One
method involves projecting a beam across a monitored area and
measuring the attenuation of the beam. Such detectors are commonly
known as `obscuration detectors`, or simply `beam detectors`.
[0004] Some beam detectors employ a co-located transmitter and
receiver with a distant reflector, and others use a separate
transmitter unit and receive a unit located on opposite sides of
the open space being monitored.
[0005] An exemplary, conventional beam detector is shown in FIG. 1.
The detector 10 includes a light source and detector 12 and a
reflector 14 placed either side of a monitored area 16. Incident
light 18 from the light source and detector 12 are projected toward
the reflector 14. The reflector 14 reflects the incident light 18
as reflected light 20 back toward the light source and detector 12.
If particulate matter enters the monitored area 16, it will
attenuate the incident light 18 and reflected light 20 and cause
the amount of light received at the light source and detector 12 to
diminish. An alternative beam detector separates the light source
from the detector and omits the reflector and directly illuminates
the detector with the light source across the monitored area 16.
Other geometries are also possible.
[0006] Whilst the mechanism of smoke detection used by beam
detectors is sound, beam detectors commonly suffer from a number of
problems.
[0007] Firstly, beam detectors may suffer a type I (false positive)
error where foreign objects or other particulate matter, such as
dust, enters the monitored area and obscure the beam. Beam
detectors are generally unable to distinguish between the
obscuration caused by particles of interest e.g. smoke, and
obscuration which results from the presence of foreign body of no
interest e.g. a bug flying into the beam.
[0008] Secondly, beam detectors may require careful alignment at
the time of installation. Such alignment aims to ensure that in
normal conditions, free from particles, light enters the sensor so
as to capture the majority of the transmitted beam, and to in turn
maximise sensitivity to an obscuration. This calibration may be
slow and therefore costly to perform. Moreover, it may need to be
repeated as the physical environment changes, for example because
of small movements in the structure to which a beam detector is
attached. In some cases, if the intensity of incident light on the
detector diminishes quickly this misalignment may also cause a
false alarm.
[0009] The inventors have proposed a system to address some of
these drawbacks in Australian provisional patent application
2008902909, filed 10 Jun. 2008 in the name of Xtralis Technologies
Ltd and International Patent application PCT/AU 2009/000727. An
exemplary embodiment described therein and reproduced as FIG. 2
herein includes a light source 32, a receiver 34, and a target 36,
acting in cooperation to detect particles in a monitored area 38.
The target 36, e.g. a corner cube reflects incident light 40,
resulting in reflected light 32 being returned to receiver 34. In
the preferred embodiment the receiver 34 is preferably a video
camera or other receiver having an array of light sensors e.g. one
or more CCD (charge-coupled device) image sensors, or CMOS
(complementary metal-oxide-semiconductor) image sensors, or indeed
any device capable of recording and reporting light intensity at a
plurality of points across its field of view.
[0010] In this system the receiver 34 receives all of the light in
its field of view 40, and includes imaging optics to form an image
of a field of its view 40, including the target 36 on its image
sensor. Receiver 34 records the intensity of light in its field of
view, in the form of data representing the image intensity at a
series of locations throughout the field of view. A portion of this
data will correspond, at least partially, to reflected light 42. A
microcontroller 54 analyses the image data, and determines which
portion of the data provides the best estimate of reflected light
42. Because the receiver 34 has a wide field of view and has the
ability to independently measure light at a wide range of points
within this field of view the light source 32 need not be carefully
aligned with target 36, or with receiver 34, since the effect of a
misalignment will simply be that a different portion of data,
corresponding to different pixels within the view, will be used to
measure the reflected light 42. Accordingly, provided that the
field of view of the receiver includes target 36, one or more
regions of interest within the image will include a measured value
for the reflected light 42.
[0011] If smoke or other particulate matter enters monitored area
38, it will obscure or scatter incident light 40 or reflected light
42. This obscuration or scattering will be detected as a drop in
the intensity for received reflected light 42 measured in the image
region determined by the microcontroller.
[0012] Pixels falling outside the region selected by the
microcontroller, to include the reflected light 42, can be ignored
as light received by these pixels does not correspond to the
reflected light 42.
[0013] Over time, as the building moves or other factors alter the
geometry of the system, the target 36 will still be in the field of
view of the receiver 34 however, the image of the target 36 will
appear at a different point on the image detector of the receiver
34. In order to address this motion, the microcontroller can be
adapted to track the image of the target 36 across its light sensor
over time to enable a smoke detection to be performed on the
correct image regions over time.
[0014] In some embodiments described therein the target 36 is
illuminated at two (or more) wavelengths .lamda..sub.1 and
.lamda..sub.2 e.g. an infrared (IR) and ultraviolet (UV) wavelength
which are emitted by corresponding light sources (or a common
source) along two substantially collinear paths.
[0015] The wavelengths are chosen such that they display different
behaviour in the presence of particles to be detected, e.g. smoke
particles. In this way the relative change in the received light at
the two (or more) wavelengths can be used to give an indication of
what has caused attenuation of the beam.
[0016] Furthermore, the applicants earlier application depicts an
embodiment capable of monitoring multiple targets simultaneously.
According to this embodiment, illustrated in FIG. 3 herein, the
detector 50 includes a light source 52, a receiver 54, a first
target 56, and a second target 57 acting in co-operation to detect
smoke in monitored area 58. Target 56 reflects incident light 62,
resulting in reflected light 64 returning to receiver 54. Target 57
reflects incident light 65, resulting in reflected light 67
returning to receiver 54. As with the previous embodiment, the
receiver 54 communicates the image data to a microcontroller 74.
Microcontroller 74 analyses the data, and determines which portion
of the data contains information most strongly related to reflected
light 64 and reflected light 67 respectively. At the conclusion of
this decision process, the microcontroller 74 will have selected
two portions of data, corresponding to respective individual pixels
or respective groups of pixels read from its image sensor, that can
most reliably be used to measure the intensity of reflected light
64 and reflected light 67 respectively. In this way the system 50
can, by the addition of only an additional target or light source,
perform the function of two beam detectors.
[0017] Using such a system, present inventors have previously
proposed a particle detection system which addresses the seemingly
contradictory requirements of the need for high sensitivity and the
need for a wide angular range of operation in a beam detection
system. However, these constraints as well as constraints on the
intensity of light sources able to be used as transmitters mean
that there may be a need to further enhance the particle detection
system in these respects.
[0018] In beam detectors the transmitted light intensity may be
limited. For example, there may be budgetary considerations which
mean that a relatively low power light emitter must be selected in
the product. Furthermore, in some cases, a limited electrical power
supply is available, especially if the transmitter unit is powered
by a battery. Eye safety is also a factor in limiting the
transmission power of the light source as is the potential nuisance
effect of visible light from the transmitter. For any of these
reasons, a relatively low transmitted signal power may be used in a
beam detector. Consequently, the signal to noise ratio of the
system may be compromised.
[0019] In order to operate satisfactorily whilst keeping the
emitted power as low as possible it is advantageous, for
sensitivity purposes, that the polar emission pattern of the
transmitter and the viewing angle of the receiver are kept as
narrow as possible. However, for installation and alignment
purposes it is advantageous that the same angles are kept as broad
as possible. Accordingly, accommodating these seemingly
contradictory requirements of the system can present problems.
[0020] A further problem that may arise in such a system is that a
reflective surface may provide one or more unintended light paths
between the transmitter and the receiver, and so interfere with
either the recognition of the direct light path, or cause
uncontrolled and unintended contributions to the received
signal(s), or both. This effect is exacerbated if the reflective
surface is subject to any changes, such as movement with
temperature or building wind loads; or the movement of people or
vehicles that causes its reflected contribution to vary over
time.
[0021] Since beam detector components are often mounted just below
a substantially flat ceiling, this type of undesired reflection may
be common. It has been realised by the inventors that to cause such
an issue, the finish of the reflective surface does not need to be
obviously reflective or mirror-like, and that even a common
matt-painted surface may provide a relatively strong specular
reflection at the narrow angle of incidence, such as would
typically occur in a beam detector with a long span mounted near a
surface. While a mirror like, or gloss finish is the extreme case,
even an apparently rough surface may give enough specular
reflection to create these problems.
[0022] Adjacent walls, particularly glazed walls, may also create a
similar issue with the additional complication that blinds or
open-able windows may be used at various times. However, this issue
does not arise as commonly, since it is rarely required that beams
are directed in close proximity to walls.
[0023] For this reason and others, beam detectors typically require
careful alignment at the time of installation. Such alignment aims
to ensure that in normal conditions, free from particles, light
enters the sensor so as to capture the majority of the transmitted
beam, and to in turn maximise sensitivity to an obscuration. This
calibration may be slow and therefore costly to perform. Moreover,
it may need to be repeated as the physical environment changes, for
example because of small movements in the structure to which a beam
detector is attached. In some cases, if the intensity of incident
light on the detector diminishes quickly this misalignment may also
cause a false alarm.
[0024] Since beam detectors are typically mounted to a wall or like
flat surface it is generally not possible to get behind the
detector in order to use a line of sight type alignment device.
Also, since detectors are usually mounted at high elevations and in
inaccessible locations, the problem of achieving accurate
alignment, and the difficulties caused by misalignment, are
exacerbated.
[0025] As discussed in relation to FIG. 1, some beam detectors
employ a co-located transmitter and receiver with a remote
reflector. Another arrangement, as illustrated in FIG. 9, uses a
light source 1102 that is remote from the receiver 1104. The
separate transmitter 1102 may be battery powered in order to avoid
the requirement for costly wiring. Furthermore, in embodiments that
are powered from the fire alarm loop the detector unit 1104 (Or the
combined light source and detector 102, of FIG. 1,) may also employ
a battery to act as a reserve supply for periods of high power
consumption that exceed a specified limit of capacity of a wired
loop supply.
[0026] In order to achieve the required service life, and for
conformance with safety requirements, it is desirable that the
battery-powered units should not be powered on during shipping or
in long-term storage.
[0027] Conventionally, battery-powered equipment is often activated
using a manual switch, or by removal of an insulating separator, or
by inserting the batteries into the equipment. The inventors have
identified that these methods have several disadvantages,
particularly in the case of beam-detection systems. The
conventional systems for powering up the battery-powered equipment
are not automatic and, in consequence, may be overlooked when the
beam-detection system is installed. In beam-detection systems the
wavelengths used for the light source 102, 202 are often invisible
to the human eye. This makes it difficult to confirm that the light
source 102, 202 is active when installed. In addition, the beam
detection systems are often installed at a significant height,
requiring scaffolding or a cherry-picker to access the system
components. As a result, it is time-consuming and costly to access
and rectify a unit that has inadvertently been left
non-operational.
[0028] Some of the conventional techniques of activating
battery-powered units also interfere with the common requirement
that beam-detection systems should avoid arrangements that cause
penetrations through the main enclosure of the unit. It is often
the case that transmitters are designed to be resistant to the
entry of dust and moisture, and the use of manually-operated
switches may makes this isolation more difficult and costly to
achieve.
[0029] A further problem that may arise with beam detectors is that
their exposed optical surfaces may become contaminated with dirt
over time. This can gradually reduce the received signal with the
potential to be raise a false alarm. Methods to avoid and remove
dirt build up on optical surfaces are known, and employed
particularly commonly in the field of closed circuit TV security
surveillance applications, such as the use of
contamination-resistant coatings on viewing windows, protective
shrouds, wash-wipe mechanisms and the like.
[0030] Also, as described in PCT/AU2008/001697 in the name of
Xtralis Technologies Limited, there are other mechanical means for
cleaning or avoiding dirt build up on optical surfaces, including
methods using filtered clean air as a barrier, or electrostatic
guard areas to prevent window contamination. Such methods may
advantageously be used for beam detectors separately or in
combination with other aspects of the current invention, and each
constitute an aspect of the present invention.
[0031] With the dual wavelength system described in connection with
FIGS. 2 and 3 a variation in the absolute intensities of received
light is tolerated to an extent, because a differential measure is
used to detect particles in the beam, but relative variation
between the wavelengths may create faults or, worse still, false
alarms; specifically a relative reduction in the received signal
from the UV beam compared to the IR beam may be mistaken for smoke.
Thus any wavelength selective build up of contaminants on the
optical surfaces can be problematic.
[0032] It is a problem in the field of video surveillance, and
similar fields which have remotely located optical devices (such as
cameras), that insects or other foreign bodies may from time to
time land on the exposed surfaces of the optical components of the
system and partly or totally obscure the field of view of the
optical components. Similar problems may also arise in particle
detection systems like beam detectors which are exposed to bugs and
other foreign bodies. Accordingly, there is a need to protect
components of particle detection systems such as a beam detector
and thereby to avoid or minimise false alarms caused by such
circumstances.
[0033] As described above, some embodiments of the present
invention may include separate light emitters in the transmitter
which are configured to emit light in different wavelength bands.
Most preferably the light emitters are LEDs. Over time the output
of the LEDs may vary in either absolute or comparative intensity or
both. With the dual wavelength system variations in absolute
intensity can be tolerated to a certain extent so long as the
relative measure of intensity used by the system for detecting
particles remains substantially constant. However, relative
variations in the output intensities of the two light emitters may
create faults or false alarms. This is particularly the case when
the output signal from the UV LED reduces compared to the output of
the infrared LED.
[0034] It is known to use beam detectors to monitor large areas by
using beams over say, 150 metres long or, in relatively confined
spaces requiring a beam length of eg. only 3 metres. In
conventional beam detector systems an identical light source and
receiver can be used for these two very different applications,
i.e. 150 metre separation or for 3 metre separation. This is made
possible by either adjusting the gain on the receiver or turning
down the transmitter power according to the separation between the
transmitter and the receiver.
[0035] However, the applicant's previous applications discussed
above, and the example of FIG. 3 show a beam detector which may
include more than one transmitter for each receiver. This presents
its own particular problems, in that it is possible to have
multiple transmitters set at vastly different distances from the
receiver. For example, consider a room of the type illustrated in
FIG. 57. This room 5700 is generally L-shaped and has a receiver
5702 mounted at the external apex of the L-shape. Three
transmitters 5704, 5706, 5708 are positioned around the room 5700.
The first transmitter 5704 is located along one arm of the L. A
second transmitter 5706 is located in a position 90.degree. from
the first receiver 5704 at the end of the other arm of the L. A
third transmitter 5708 is mounted across the apex of the L-shape
from the receiver 5702. As will be appreciated the distances
between the transmitters 5704 5706 and the receiver 5702 are much
longer than the distance between the transmitter 5708 and the
receiver 5702. As a result, the level of light received from each
transmitter will be very different. Moreover transmitter 5708 may
be so close to the receiver that it saturates its light receiving
element.
[0036] Other disadvantages may also arise, for example, from time
to time, an installer may take advantage of the reliable
performance of beam detectors and install a system outside the
manufacturer's specifications. For example, although beam detectors
are often intended to operate with a substantial separation between
the transmitter and receiver an installer may extend this distance
to provide a system beyond that recommended by the manufacturer or
allowed by regulations. In some cases an installer of the particle
detector may not know of the limits of operation of the receiver
for the light source provided therewith.
[0037] In such circumstances an installed particle detector may
operate satisfactorily at initial installation, but sometime
following installation, cease to operate correctly. This may occur,
for instance where the particle detector or was initially installed
close to, but beyond its design limits. Over time, changes may
occur to the equipment or environment, which gradually alter the
received signal strength due to reasons other than the presence of
particles in the beam. These changes may be caused by, for example,
component ageing, gross alignment drift, or contamination of
optical surfaces. Such system drift would ordinarily be handled by
the system if it had been set-up within its design limits. However,
when the system is set up outside these limits, degradation of
performance and the associated occurrence of fault conditions may
occur prematurely or repeatedly.
[0038] Furthermore, it is desirable to be able to calibrate and/or
test such a beam detector by simulating the presence of smoke using
a solid object. Such a test is a requirement of standards bodies
testing for beam detectors. For example, the European EN 54-12
standard for `Biodetection and fire alarm systems. Smoke detectors.
Line detectors using an optical light beam`.
[0039] In prior art testing methods the testing of beam detectors
employs a light filter that partially obscures the projected light
beam to simulate the effect of smoke. The filters used usually
consist of a mesh of fibres, or dye-loaded plates or transparencies
with printed features which obstruct all visible and near visible
wavelengths by substantially the same amount in a repeatable
fashion. The present inventors have realised that this type of
filter may not be suitable for use with a beam detector of the type
described above.
[0040] In a preferred embodiment of the system described in FIGS. 1
to 3, the light sources are configured to include a plurality of
light emitters, wherein each light emitter is adapted to generate
light in a particular wavelength band. Moreover, the separate light
sources are arranged to emit light at different times in order that
a monochromatic imaging element may be used. The direct result of
the use of separate light emitters is that there is some separation
between the two light emitters in the light source, and thus the
light will travel over slightly different, although closely
adjacent, beam paths through the intervening space between the
light source and receiver. This provides a risk that a small object
such as an insect on the transmitter could affect one light path
more than the other and so affect the reading of the receiver. This
may induce a false alarm or unnecessary fault condition.
[0041] Conventional beam detectors require careful alignment at the
time of installation. Such alignment aims to ensure that in normal
conditions, free from particles, light enters the sensor so as to
capture the majority of the transmitted beam, and to in turn
maximise sensitivity to an obscuration. This calibration may be
slow and therefore costly to perform. Moreover, it may need to be
repeated as the physical environment changes, for example because
of small movements in the structure to which a beam detector is
attached. As stated above, the inventors have previously proposed a
particle detector in PCT/AU 2008/001697, filed 10 Jun. 2009 in the
name of Xtralis Technologies Ltd (the specification of which is
incorporated herein, by reference, in its entirety) which includes
a receiver which has a light sensor comprising matrix of light
sensor elements, e.g. CCD (charge-coupled device) image sensor
chip, or CMOS (complementary metal-oxide-semiconductor) image
sensors such as in a video camera, or other receiver that is
capable of receiving and reporting light intensity at a plurality
of points across its field of view. Each sensor element in the
receiver produces a signal that is related to the intensity of the
light that it receives. The signals are transmitted to the
controller, where a particle detection algorithm is applied to the
received image data. Compared to a single-sensor receiver, the
receiver in this particle detector has a wider field of view but
lower noise and has the ability to independently measure light at a
wider range of points within this field of view.
[0042] Because each sensor element has an inherent noise level, the
overall signal-to-noise ratio of the system can be improved by
focusing the target (i.e. beam image) on a single sensor element.
However, this may not yield optimal results.
[0043] The above mentioned type of sensor e.g. CCD's and the like,
are sometimes subject to a phenomenon created by the image
processing algorithm used for the receiver, known as staircasing,
wherein adjacent pixels or adjacent groups of pixels have
significantly different values. The physical structure of the
sensor also has non-responsive "gaps" between sensor elements that
produce no signal. Because of these effects, any variation in the
alignment of the smoke detector components can potentially create a
large variation in the measured light intensity level.
[0044] For example, because of the small size of the focused
target, a very small movement of the receiver or the transmitter
could cause the target to move onto an entirely different sensor
element with a very different inherent noise level or response
compared to the previous pixel on which it was focused. It may also
fall into a position, where all, or a non-trivial part, of the
received beam falls into one of the aforementioned "gaps". The
resulting variation in the image intensity as determined by the
controller can thus potentially cause the controller to falsely
detect smoke.
[0045] To partly ameliorate this problem, the detector can be
adapted to track the target across the light sensors over time to
enable a smoke detection to be performed on the signals from the
correct sensors over time. However, to properly determine the image
intensity, the controller will be required to ascertain the
inherent properties of different light sensors used over time.
Doing so requires system resources such as processing cycles and
power. Also it is not always possible for the controller to make
this determination.
[0046] In beam detectors an additional problem that may arise is
interference from ambient light within the volume being monitored.
The ambient light can either be from sunlight illuminating the
volume or artificial lighting used to illuminate the space.
Accordingly, beam detectors require mechanisms for minimising the
impact of this light. This problem is compounded by the conflicting
requirement that the light sources of the beam detector should be
relatively low powered so that they minimise power consumption, are
eye safe and do not create a visible nuisance. In prior art beam
detectors which use a single wavelength of light a filter is
typically used to reduce the signal from ambient light. In the case
of an infrared beam detector this is generally a low pass filter
that removes substantially all visible and UV light. However, this
is inappropriate for a multiple wavelength system as described
herein.
[0047] In the preferred embodiment of the system described above
the particle detector is powered at the receiver directly from the
fire alarm loop. This minimises the installation costs of the
device in that it obviates the need for dedicated wiring for
supplying power or communicating with the detector. However, the
fire alarm loop usually only provides a very small amount of DC
electrical power for the detector. For example, an average power
consumption of about 50 mW may be desirable for such a detector.
However with current technology the power consumed during video
capture and processing may be far above the 50 mW that is available
from the loop. To address this problem a separate power supply
could be used, but this is costly since standards for fire safety
equipment are onerous, e.g. they require a fully approved and
supervised battery backed supply, and fixed mains wiring.
[0048] The limited supply of power also limits the optical power
output of the transmitter. The limited optical power output in turn
limits the signal to noise ratio of the measured signal. If the
signal to noise ratio of the system degrades too far, the system
may experience frequent or continual false alarms.
[0049] In some systems, the signal to noise ratio can be enhanced
by employing long integration or averaging times at the receiver.
However system response times, which are usually between 10 and 60
seconds, must be increased to higher levels if long integration
times are used. This is undesirable.
[0050] In addition to using a beam detector for smoke detection it
is often desirable to use other sensor mechanisms for detecting
additional or alternative environmental conditions or hazards, for
example CO.sub.2 gas detection or temperature detection. The
detectors conventionally use a wired or radio communication link to
signal an alarm or fault condition to fire alarm control panel or
like monitoring system. As such these links often add significant
cost and potential reliability issues to the alarm system.
[0051] In some systems the present inventors have determined that
it can be beneficial to operate at least some components, and most
advantageously the transmitter on a battery. An exemplary component
is described in the applicant's co-pending patent application no.
PCT/AU 2009/000727, filed on 26 Jun. 2008, the contents of which
are incorporate herein by reference for all purposes.
[0052] However, a problem that can arise in a battery powered
component of a particle detector is that over time, the batteries
of the component will become discharged and the component will
ultimately fail. Such failure will potentially require an
unscheduled maintenance call out for the device to be repaired and
recommissioned. In a smoke detection application this is
particularly problematic as the equipment is used in a life-safety
role and faults are required to be rapidly remedied. The problem
can be remedied by performing preventative maintenance but
ultimately this may amount to performing unnecessary servicing and
replacement of units that have a significant amount of battery life
remaining and therefore is costly and wasteful of materials.
[0053] Unfortunately, variations in individual battery performance
and environmental conditions make simply scheduling routine
replacement periods unreliable and potentially wasteful. One
apparent solution to the problem is to equip the component with an
indicator of battery state, however this has a disadvantage of
adding cost, and the indicator itself is power consuming which
further reduces battery life. Moreover, it requires regular direct
inspection of the indicator on the component which, in the case of
a beam detector, may be particularly inconvenient.
[0054] In beam detectors such as that described in relation to FIG.
3 i.e. where a plurality of beam detectors are formed by
corresponding transmitter and receiver pairs, such that two or more
beams either intersect or pass through a common region of air,
sufficiently close to each other that their points of intersection
can be mapped to addresses within the region being monitored, a
problem may arise in that any one of the subsystems may be affected
by environmental conditions or system problems that do not affect
the other subsystem. Such issues generally force a reduction in
achievable sensitivity or increase the rate of unwanted false
alarms.
[0055] Reference to any prior art in the specification is not, and
should not be taken as, an acknowledgment or any form of suggestion
that this prior art forms part of the common general knowledge in
Australia or any other jurisdiction or that this prior art could
reasonably be expected to be ascertained, understood and regarded
as relevant by a person skilled in the art.
SUMMARY OF THE INVENTION
[0056] In a first aspect, the present invention provides a beam
detector arrangement comprising a transmitter adapted to transmit
one or more beams of light having a predetermined characteristic
over a field of illumination and a receiver having a field of view
of the receiver and adapted to receive a beam of light transmitted
by the transmitter;
[0057] the beam detector being installed to protect a monitored
volume which includes a structure having one or more reflective
surfaces within the field of illumination of the transmitter and
the field of view of the receiver;
[0058] the beam detector including a processor adapted to determine
whether a light beam received at the receiver possesses one or more
predetermined light characteristics.
[0059] In the event that the one or more characteristics are
possessed the processor can be adapted to determine that a beam of
light from the transmitter is received. In the event that a
received beam does not possess the one or more characteristics the
processor can determine that a beam of light from the transmitter
is not received. Alternatively the processor can determine that the
beam of light received is a reflection of the transmitted beam.
[0060] The beam detector arrangement can include signalling means
adapted to signal a fault condition in the event that the processor
determines that a beam of light from the transmitter is not
received and/or a reflected beam is received.
[0061] In a second aspect the present invention provides a method
for determining whether a beam of light received by a receiver of a
beam detector is a directly transmitted beam or a reflected beam.
The method including receiving the beam at a receiver and measuring
one or more predetermined characteristics of the beam, and
depending on the extent to which the predetermined characteristic
is present in the beam determining if the received beam is a
directly transmitted beam or a reflected beam. In the event that
the one or more characteristics of the received beam do not
substantially match one or more predetermined characteristics of
the transmitted beam the method can include, determining that the
received beam is a reflection. The beam characteristics can include
relative strength of two or more wavelength components in the
received beam and/or received polarisation characteristics of the
beam.
[0062] In a further aspect the present invention provides a
receiver for a beam detector, the receiver including the plurality
of image sensors, each image sensor including a plurality of sensor
elements, said image sensors being arranged to have at least
partially overlapping fields of view. The receiver can additionally
include an optical arrangement adapted to form an image on each of
the two sensors. The receiver can additionally include image
analysis means to analyse an image from more than one of the
plurality of image sensors to determine an angular position of an
image component within the field of view of a plurality of the
sensors. The image component can be one or more beams transmitted
by a light source of a beam detector.
[0063] In a further aspect the present invention provides a
receiver for a beam detector, the receiver including: [0064] one or
more sensors including a plurality of sensor elements to receive a
beam of light from a transmitter; [0065] processing means in data
communication with the one or more sensors to receive and process
image data therefrom; and [0066] input means adapted to receive an
input representative of a number of beams which are to be received
from one or more transmitters of the beam detector.
[0067] Preferably, the input means can include one or more switches
(e.g. DIP switches), or by providing a data input interface such as
a serial port, or the like, over which data may be provided to the
processor means, or memory associated therewith.
[0068] In a further aspect, the present invention provides a beam
detector including: one or more light sources adapted to transmit
said beam of light across a region being monitored; one or more
receivers arranged with respect to the transmitter and the volume
being monitored such that light from the transmitter arrives at the
receiver after traversing at least a part of the volume being
monitored.
[0069] In certain embodiments of the present invention the beam
detector system may include one or more light blocking baffles
arranged with respect to the volume being monitored and the
transmitter and/or receiver such that no reflections from a surface
within a field of illumination a light source and a field of view
of a light receiver of the beam detector arrive at the
receiver.
[0070] In preferred embodiments of the beam detector the light
receiver is made in accordance with one of the aspects of the
invention described herein.
[0071] In certain embodiments of the present invention, the
transmitter of the beam detector is made in accordance with an
embodiment of any one of the aspects of the present invention.
[0072] In one aspect the present invention provides a transmitter
for a beam detector transmitter including one or more light sources
adapted to generate light in a spatially distinct beam pattern.
Preferably, the spatially distinguishable beam pattern is not
symmetrical in at least one plane. The spatially distinguishable
beam pattern can include a pattern of individual light beams having
distinguishable characteristics. The characteristics may be
wavelength characteristics, polarisation characteristics or
modulation characteristics which are distinguishable from each
other. Other characteristics may also be used. For example, in a
preferred form, this distinguishable pattern can include a pair of
distinguishable light beams. A single light source can be used in
some embodiments of the transmitter. In this case, the image of the
beam which is formed by a receiver must be such that a shape of the
light source is directionally distinguishable. For example, the
image of the light source can be `L` shaped such that up and down
and left and right can be distinguished from an image of the light
source.
[0073] In a beam detector including a transmitter of the above
type, the present invention, in a further aspect, also provides a
method of determining whether a beam received at a receiver is
transmitted by a direct or reflected path, the method including:
[0074] arranging a light source and receiver such that the beam
transmitted by the source is received at the receiver; and [0075]
orienting the light source with respect to an adjacent surface
within the field of illumination of the light source and field of
view of the receiver, such that a direct image of the light source
and reflected mirror image of the light source from the surface are
distinguishable at the receiver.
[0076] This step of aligning can include aligning the light source
such that its image is not symmetrical in the direct and reflected
images.
[0077] In a further aspect the present invention provides a method
of distinguishing a directly received beam from a reflected beam in
a beam detector system, the method including receiving an image
containing two image segments which potentially correspond to beams
transmitted by the particle detector; [0078] determining a
brightness of each of the received beams; and [0079] determining
that a brightest one of the received beams is the directly received
beam.
[0080] In a further aspect of the present invention there is
provided a method of determining which one of a plurality of
received beams is directly received from a light source and which
is received by a reflection from a surface, the method including:
[0081] determining which of the received beams is received at a
sensor element of a light sensor of a receiver of the beam detector
that is furthest perpendicularly from the reflecting surface; and
designating the determined beam image as the direct beam image.
[0082] In a first aspect there is provided a beam detector
including: [0083] a light source adapted to transmit a beam of
light with a first polarisation state; [0084] a light receiver
adapted to receive light in a second polarisation state and output
a received light level; and [0085] a controller adapted to analyse
the received light level and apply alarm and/or fault logic and if
a predetermined fault condition exists, to initiate an action.
[0086] In one embodiment the first and second polarisation states
are parallel.
[0087] In another embodiment the first and second polarisation
states are offset from each other. They may be orthogonal.
[0088] The beam detector can include a light source adapted to
transmit a second beam of light with a third polarisation state.
The first and third polarisation states are preferably different.
Most preferably they are orthogonal. The first and second light
sources can be a common light source. The third and second
polarisation states can be the same.
[0089] The beam detector can also include a light receiver adapted
to receive light in a fourth polarisation state.
[0090] The second and fourth polarisation states are preferably
different. Most preferably they are orthogonal. The fourth and
first polarisation states can be the same.
[0091] One or both of the light receiver or transmitter can include
a polarising filter, or a plurality of interchangeable filters.
[0092] A component of a beam detector system including: [0093] at
least one electro-optical component configured to emit light or
receive light in a first spatial distribution; and [0094] an
optical subsystem arranged with respect to the electro-optical
component such that the first spatial distribution is adjusted to
form a second spatial distribution, wherein [0095] the relative
extent of the first spatial distribution along two non-parallel
axes are different to the relative extent of the second spatial
distribution along the same axes.
[0096] Preferably the axes are orthogonal to each other. Most
preferably one is interdict to be a vertical axis and the other a
horizontal axis.
[0097] Preferably the second spatial distribution is relatively
wider horizontally than vertically when compared to the first
spatial distribution.
[0098] The optical subsystem can include an anamorphic lens, or
other `wide-screen` optical system.
[0099] The electro-optical component can be an image sensor. The
electro-optical component can be a light emitter e.g. an LED, laser
diode.
[0100] A further aspect of the present invention provides a light
source for a beam detector including: [0101] at least a light
emitter to generate a beam of light; and [0102] an optical
subsystem for controlling the angular dispersion of the beam of
light wherein the optical subsystem is adapted to shape the beam of
light such that it has a larger angular dispersion along one axis
than another.
[0103] Preferably the shape of the beam is wider than it is high.
The beam can be shaped such that it has a horizontal angular
dispersion of between 5 and 25 degrees. Most preferably it is
between about 10 and 15 degrees.
[0104] The vertical dispersion can be between 0 and 10 degrees.
Most preferably it is between about 3 and 5 degrees.
[0105] In a yet another aspect the present invention provides a
receiver for a beam detector including: [0106] a light sensor
capable of providing an output representative of a sensed light
level at a plurality of positions on the sensor; and [0107] an
optical subsystem adapted to receive light in a field of view
having a first shape and direct it onto the light sensor in an
image of a second different shape.
[0108] Preferably the optical subsystem includes an anamorphic
lens. The field of view of the optical subsystem is preferably
wider in one direction than another. Preferably it is wider than it
is high.
[0109] The field of view of the optical subsystem can be defined by
a maximum light acceptance angle in one direction and a maximum
light acceptance angle in another direction.
[0110] Preferably the maximum horizontal acceptance angle is 90
degrees or less. However it could be more in some cases.
[0111] Preferably the maximum vertical acceptance angle is 10
degrees or less.
[0112] A further aspect of the invention, in broad outline relates
to the set up of particle detection apparatus wherein a visual
alignment device incorporated with or attached to the particle
detection apparatus is directed towards a target and is used to
accurately align the apparatus at the time of installation, or when
adjustment of alignment is necessary. The visual alignment device
and the optical elements in the particle detector will have a fixed
alignment relative to each other. The visual alignment device may
comprise a visual beam generator which projects a visually
observable light beam towards the remote surface, or it may
comprise a video camera which receives an image of the remote
surface and displays the image of the surface on a display
screen.
[0113] One aspect of the invention provides a component of a smoke
detector comprising: [0114] an optical module including one or more
light sources and/or one or more light receivers; mounting means
for mounting the optical module to a support surface; [0115] an
articulated connection located between the mounting means and the
optical module; and [0116] a visual alignment device fixed to move
with the optical module for assisting in aligning the light source
or sources and/or receiver or receivers, relative to a target.
[0117] Optionally the visual alignment device comprises one or more
sockets in the optical module in which an alignment beam generator
can be inserted.
[0118] The articulated connection may include one or more locking
means for locking the orientation of the optical module relative to
the mounting means. The articulated connection may comprise a ball
and cup joint, capable of allowing the optical module to be tilted
relative to the mounting means through a relatively large arc of
tilt, the locking means adapted to lock the ball to the cup in a
selected orientation. The locking means may comprise a screw member
which engages in a threaded bore in the cup and contacts the
surface of the ball to lock the ball and cup together. Optionally
the screw is accessible via the visual alignment device.
[0119] In an alternative configuration of the invention provides a
component of a smoke detector comprising: [0120] an optical module
including one or more light sources and/or one or more light
receivers; [0121] fixed mounting means for mounting the optical
module to a support surface; [0122] an articulated mounting means
located between the optical module and one or more light sources or
light receivers; and [0123] a visual alignment device fixed to move
with the light source or sources and/or receiver or receivers, to
assist in aligning the light source, sources and/or receivers
relative to a target.
[0124] Optionally the visual alignment device comprises one or more
sockets in the articulated mounting means in which an alignment
beam generator can be inserted.
[0125] The articulated connection may include one or more locking
means for locking the orientation of the optical module relative to
the articulated mounting means. The articulated connection may
comprise a ball and cup joint, capable of allowing the optical
module to be tilted relative to the mounting means through a
relatively large arc of tilt, the locking means adapted to lock the
ball to the cup in a selected orientation. The locking means may
comprise a screw member which engages in a threaded bore in the cup
and contacts the surface of the ball to lock the ball and cup
together. Optionally the screw is accessible via the visual
alignment device. Alternatively a rotatable mount can be used.
[0126] The visual alignment device may comprise a laser housed in
or mounted on a cylindrical tube or shaft sized to be a sliding fit
in the beam alignment means. Optionally the laser forms part of a
tool for locking the articulated connection. The laser may flash to
assist in visual identification.
[0127] Alternatively the visual alignment device may comprise a
video camera mounted to move with the housing, and able to generate
an image of the target, the image including sighting means which,
when aligned with the target will indicate that the optical
component is operationally aligned. The housing may include a video
camera mount which, when the camera is mounted thereto aligns the
camera with the housing such that the camera has a field of view
aligned in a direction in a known orientation relative to the light
source. Optionally the known orientation is axially aligned with
light emitting from the light source.
[0128] The component can be, for example a transmitter, receiver or
target for a particle detector, such as a beam detector.
[0129] Another aspect of the invention provides a method of
aligning a component of a smoke detector comprising: [0130]
mounting the component in an initial orientation to a support
surface, the component including a visual alignment device; [0131]
determining the orientation of the component by visually observing
an output of the visual alignment device; [0132] adjusting the
orientation of the component by monitoring the visual alignment
device until the component is in a selected operating orientation;
and [0133] fixing the component in said operating orientation.
[0134] The method can include removing the visual alignment device
from the component.
[0135] The orientation of the component could be determined by
observing either of a position of an alignment light beam emitted
from the visual alignment device at a location remote from the
support surface, or observing an image of the remote surface
generated by a camera of the visual alignment device.
[0136] A further aspect of the invention provides an alignment tool
comprising: [0137] a shaft having a handle; [0138] a driver
actuatable by the handle; [0139] a visual alignment device in a
fixed or known orientation relative to the driver; and [0140] a
shaft and a handle.
[0141] Further there is provided for the visual alignment device to
comprise a laser which is located in a casing, and for a handle to
have a recess therein shaped to receive the casing. The laser will
typically be a battery powered laser with an on/off switch so that
the laser may be switched off when not in use. The shaft may be
straight or may have an elbow therein, depending on the
configuration of the apparatus with which the tool is to be used.
Alternatively the visual alignment device may comprise a video
camera.
[0142] An aspect of the invention provides a visual alignment tool
having: [0143] engagement means for engaging with and aligning the
visual alignment tool relative to a particle detector component;
and [0144] visual targeting means for providing a visual indication
of the alignment of the particle detector component when so
engaged.
[0145] The visual targeting means may be a camera, but is
preferably a means for projecting visible light. The visible light
could be a simple beam as in a laser pointer, or more complex
patterns such as cross hairs. The means for projecting may flash to
assist in visual identification. The visual targeting means is
preferably battery powered, and may include an on/off switch so
that it may be switched off when not in use.
[0146] The engagement means is preferably an elongate projection
receivable within a recess within the particle detector component.
Preferably the visual targeting means is coaxially aligned with the
engagement means.
[0147] The visual alignment tool preferably includes an elongate
handle and a shaft, the shaft projecting from an end of the handle
and being coaxially aligned therewith, wherein at least a portion
of the shaft forms the engagement means. The shaft and recess may
be cylindrical and sized for a sliding fit therebetween.
[0148] The visual targeting means is preferably arranged at the
other end of the handle. Optionally the visual targeting means may
be removable from the handle.
[0149] The visual alignment tool may include a driver for engaging
with and actuating a locking means of the particle detector
component.
[0150] The driver is preferably formed at an end of the shaft
distal from the handle and rotatable about the axis of the shaft to
actuate the locking means. The driver may be, for example, an Allen
key (hex), Phillips head or other propriety shape e.g. a triangle.
Ideally the driver is shaped for engagement with the locking means
in only a single relative rotational orientation, e.g. the drive
may be a non-equilateral triangular projection receivable in a
complementary recess, so that the rotational orientation of the
visual alignment tool is indicative of the state of the locking
means. Visible indicia may be provided on the tool to aid in said
indication.
[0151] In this aspect the invention also provides a particle
detector component; [0152] the component including a mounting
portion, an optical module, and locking means; [0153] the mounting
portion being fixedly attachable to a mounting surface; [0154] the
optical module being articulated relative to the mounting portion
for alignment relative to a target and including means for enabling
a visual indication of said alignment; and [0155] the locking means
being actuatable to lock the optical module relative to the
mounting portion in a selected alignment.
[0156] The term `target` as used herein is intended to be
interpreted broadly, and may include an actual target mounted at
the remote location for reflecting the source light back to a
receiver. The target may also however simply refer to a remote
surface if reflected light from that remote surface is monitored by
the receiver or even a desired point on which a component should be
aligned, e.g. the receiver could be a target for a light source or
vice versa.
[0157] The means for enabling a visual indication could be a visual
targeting means, including an electro optical device such as a
camera or laser pointer, but is preferably an engagement feature
for cooperating with a visual alignment tool incorporating visual
targeting means.
[0158] Preferably the optical module includes an elongate recess
forming the engagement feature. The recess preferably has at least
one open end and is arranged so that the axis of the recess
projects toward the target when the optical module is in alignment
with it. The recess may project in a direction parallel to a limit
of a field of operation of the optical module or in some other
known physical relationship with the spatial optical
characteristics of the optical module.
[0159] The locking means is preferably actuatable by the visual
alignment tool. The locking means preferably includes a driven
member located within the recess and engageable with a driver of
the visual alignment tool to actuate the locking mechanism.
Preferably it is adapted to be rotationally driven about the axis
of the recess to a selected orientation to actuate with locking
means. The driven member is preferably shaped for engagement with
the driver of the visual alignment tool in only a single relative
rotational orientation, e.g. the driver may a non-equilateral
triangular projection receivable in a complementary recess formed
in the driven member, so that the rotational orientation of the
visual alignment tool is indicative of the state of the locking
means. Indicia may be provided on the component to aid in said
indication.
[0160] Preferably one of the optical module and the mounting
portion, most preferably the optical module, is captured within the
other portion, said articulation being effected by a spherical
sliding fit between the optical module and the mounting portion.
The driven member may be a grub screw within one of the optical
module and mounting portion, and rotatable to engage the other of
the optical module or mounting portion. But preferably, the optical
module includes a brake shoe and a cam, wherein the cam is arranged
to be driven by the driven member and in turn drive the brake shoe
to, frictionally or otherwise, engage the mounting portion and
thereby lock the optical module relative to the mounting portion.
The cam may be attached to the driven member or integrally formed
therewith. The braking shoe may be biased towards a retracted,
non-braking, position.
[0161] The optical module may include a simple optical element,
such as a lens or a mirror. For example, a mirror alignable for
redirecting a beam to or from a fixedly mounting electro-optical
element. In this case the mirror and electro-optical element may be
mounted in a housing.
[0162] Preferably the optical module includes an electro-optical
element such as a light emitting element or elements or light
receiver. The electro-optical element could be camera.
[0163] Preferably the particle detector component is configured to
operatively connect a circuit, to enable operation of the
electro-optical element, to a power supply when said locking means
is actuated. For this purpose, a switch may be associated with the
driven member. For example, the driven member may carry at a point
at a radius from its axis a magnet which is arranged to act on a
reed switch when the driven member is rotated to the selected
orientation.
[0164] This aspect of the invention also provides a combination of
the particle detector component and the visual alignment tool, and
methods of installing, and aligning, a particle detector
component.
[0165] There is provided a method of aligning a particle detector
component, the particle detector component includes an optical
module, a mounting portion and locking means, the method includes:
[0166] articulating the optical module relative to the mounting
portion to align a visual indication of orientation with a
target.
[0167] Preferably the method includes actuating the locking means
to lock the optical module in said alignment.
[0168] Preferably the method further includes engaging with the
optical module of the particle detector component a visual
alignment tool to provide said visual indication of the orientation
of the optical module; and, [0169] disengaging said visual
alignment tool.
[0170] Said actuation preferably includes rotating said visual
indication tool, and most preferably simultaneously connects an
electro-optical component to a power supply.
[0171] The method of installing the particle detector component
includes: [0172] fixedly mounting a mounting portion of the
particle detector component to a mounting surface;
[0173] and [0174] aligning the particle detector component in
accordance with the aforedescribed method.
[0175] In a preferred form the step locking the optical module and
connecting the electro-optical component to a power supply.
[0176] In another aspect the invention provides a smoke detector
component: [0177] the component including a mounting portion, an
optical module, locking means and activation means; [0178] the
mounting portion being fixedly attachable to a mounting surface;
[0179] the optical module including a electro-optical element and
being articulated relative to the mounting portion for alignment
relative to a target; [0180] the locking means being actuatable in
response to an installer input to lock the optical module relative
to the mounting portion in a selected alignment; and [0181] the
activation means configured to operatively connect the
electro-optical element to a power supply in response to said
installer input.
[0182] In a further aspect the present invention provides, a
component of a particle detector including an electro-optical
component adapted to at least transmit or receive an optical signal
over an angular region, an optical assembly adapted to redirect an
optical signal said optical assembly an electro-optical component
being mounted relative to each other such that the electro-optical
component receives or transmits optical signals via the optical
assembly, wherein: the orientation of the optical assembly is
adjustable with respect to the electro-optical component to enable
the direction of optical signals transmitted or received by the
component to be changed.
[0183] Preferably the component includes a housing in which the
electro-optical component and optical assembly are mounted; and an
aperture through which an optical signal may pass.
[0184] The mounting means can be adapted to mount the optical
assembly rotably with respect to the housing. The mounting means is
preferably a friction fit with a recess in the housing. The
mounting means preferably includes an engagement means engagable by
a actuating tool to allow rotation of the optical assembly. The
engagement means can be adapted to engage with an actuating tool as
described herein.
[0185] The optical assembly can include a mirror to reflect an
optical signal.
[0186] The electro-optical component can be a light sensor
including a plurality of sensor elements. The light sensor is
preferably a camera adapted to capture a series of images.
[0187] According to an aspect of the invention there is provided a
particle detector assembly comprising a first module having an
actuator and a second module configured to be mounted to the first
module. The second module comprises electro-optical system for use
in a beam-detection system and a power source operable to provide
electrical power to the electro-optical system. The second unit
also includes a switch responsive to the actuator. When the second
module is mounted to the first module, the actuator causes the
switch to operatively connect the power source to the
electro-optical system.
[0188] In one arrangement the actuator is a magnet, and a reed
switch is used to detect the proximity of the magnet when the two
modules are assembled.
[0189] In broad concept, one aspect of this invention, may improve
system performance in cases where contamination of the optical
surface affects both wavelengths by substantially the same amount.
In this aspect, very gradual reduction of the received signals are
compensated by an increase of the effective overall receiver gain
of both signal channels, using a time constant that is chosen to be
far longer than might cause a real fire to go undetected; for
example a week.
[0190] Thus, in one aspect the present invention includes detecting
a long time drift in received light level in a particle detection
system; and increasing gain of a detection circuit to compensate
for the drift. In a system with multiple illuminations, e.g. at
different wavelengths a wavelength dependent gain increase can be
made.
[0191] This concept can be extended such that where the
contamination of the optical surface affects the shorter wavelength
by more than it does the longer wavelength, as may occur when the
contamination consists largely of very small particles such as are
present as a result of smoke pollution, the very gradual reduction
of the received signals are individually compensated by an increase
of the effective overall receiver gain of each signal channel
separately, again using a time constant that is chosen to be far
longer than might cause a real fire to go undetected; for example a
week.
[0192] In a first aspect the present invention provides a light
source for use in a particle detection system, the light source
adapted to transmit: a first light beam in a first wavelength band;
a second light beam in a second wavelength band; and a third light
beam in a third wavelength band, wherein the first and second
wavelengths bands are substantially equal and are different to the
third wavelength band.
[0193] The first and second wavelength bands may be in the
ultraviolet portion of the EM spectrum. The third wavelength may be
in the infrared portion of the EM spectrum.
[0194] The location from which the first light beam is transmitted
from the light source may be separated from the location from which
the second light beam is transmitted from the light source. The
separation may be approximately 50 mm.
[0195] The light source may further include a first light emitter
for emitting the first and second light beams and a second light
emitter for emitting the third light beam. In this case the light
source may further include a beam splitter for splitting light
emitted from the first light emitter into the first and second
light beams. Alternatively, the light source may include a first
light emitter for emitting the first light beam, and a second light
emitter for emitting the second light beam, and a third light
emitter for emitting the third light beam. The first, second and/or
third light emitters may be light emitting diodes.
[0196] The light source may further include a controller, the
controller configured to generate the first, second and third light
beams in a repeated sequence. Preferably the repeated sequence
includes the alternate operation of the first, second and/or third
light emitters.
[0197] In a further aspect the present invention provides a light
source for use in a particle detection system, the light source
including: a first light emitter for emitting a first beam of
light; a second light emitter for emitting a second beam of light;
and an optical system including a transmission zone from which
light from the first and second light emitters is transmitted from
the light source, wherein the optical system is arranged such that
obstruction of the transmission zone by a foreign body results in a
substantially equivalent obstruction of both the first and second
beams of light.
[0198] The first and second light emitters can be semiconductor
dies. Preferably they are semiconductor dies housed within a single
optical package.
[0199] The optical system can further include light directing
optics for directing the first and second beams of light from the
first and second light emitters to the transmission zone.
[0200] The light directing optics may be selected from a group
including, but not limited to, a convex lens, a Fresnel lens, and a
mirror. Other optical components or combinations thereof can be
used.
[0201] The transmission zone is preferably forms at least a part of
an externally accessible optical surface of the optical system. For
example the outside surface of a lens, mirror, window, LED package
or the like.
[0202] The optical system may further include beam shaping optics
adapted to modify a beam shape of either or both of the first and
second beams of light.
[0203] The beam shaping optics may provide light transmitted from
the light source with a beam divergence of approximately 10
degrees.
[0204] In this case the beam shaping optics may modify the beam
shape of either or both of the beams to extend further in one
direction than another, e.g. further horizontally than
vertically.
[0205] The beam shaping optics can also modify the first and second
beams so that they have a different beam shape to each other. The
beam shaping optics may modify the first beam of light to have a
wider beam shape than the second beam of light.
[0206] The beam shaping optics may include one or more beam
intensity adjusting elements configured to adjust the spatial
intensity of the beam. Beam intensity adjusting elements may be
selected from a group including, but not limited to, an optical
surface coating, a ground glass diffuser, and an etched glass
diffuser.
[0207] The first light emitter may emit an ultraviolet light beam
and the second light emitter may emit an infrared light beam.
[0208] The light directing optics and beam shaping optics can be
combined into a single optical element, or comprise an optical
arrangement with multiple optical elements. The optical elements
can be transmissive or reflective elements.
[0209] In a further aspect the present invention provides a
particle detection system including a light source and a receiver,
the light source as described in any one or more of the above
statements.
[0210] A light source for a particle detector, including: one or
more light emitters adapted to generate at least one light beam
having a first apparent size from a distant point of view; an
optical system arranged to receive the at least one light beam and
transmit the at least one light beam and adapted to cause the
transmitted light beam to have a second apparent size larger than
the first apparent size from the distant point of view.
[0211] The optical system preferably includes a beam diffuser. The
diffuser can be a dedicated optical component (e.g. a piece of
etched glass) or formed as a surface treatment on an optical
component that is used for another purpose.
[0212] In another aspect, there is provided, a light source for a
particle detector, including: one or more light emitters adapted to
generate at least one light beam having components in at least two
wavelength bands, and optionally an optical system through which
the one or more beams pass; the light emitter(s) and or optical
system being configured to cause light in one of the at least two
wavelength bands to have a spatial intensity profile which is
different to light in another of the wavelength bands.
[0213] Preferably the beam width of light in one wavelength band is
wider than the beam width of light in another wavelength band.
Preferably light in a longer wavelength wavelength band has a
narrower beam width than light shorter wavelength wavelength band.
Preferably the longer wavelength band includes the infrared or red
portion of the EM spectrum. The shorter wavelength band can include
light in the blue, violet or ultraviolet portion of the EM
spectrum.
[0214] In yet another aspect, the present invention provides a
light emitter usable in a particle beam detector, the light emitter
including: housing including a window portion through which light
is emitted; means to generate light in a plurality of wavelength
bands; and a light sensitive element arranged within the housing
and configured to receive a portion of the light in at least one or
more of the wavelength bands emitted by the means to generate
light; one or more electrical contacts for enabling electrical
connection between the means to generate light, the light sensitive
element and an electrical circuit.
[0215] Preferably the light emitter includes a plurality of light
emitting elements adapted to emit light in a corresponding
wavelength band.
[0216] The light sensitive element can be a photo diode or other
light sensitive circuit element.
[0217] Most preferably the light emitter elements are LED dies.
Preferably the window portion of the housing can be adapted to
control the shape of a beam of light emitted.
[0218] The housing can be an LED package.
[0219] In one form the light emitter includes a plurality of light
emitters for emitting light in one or more of the wavelength bands.
The plurality of light emitters can be arranged within the housing
to achieve a predetermined beam characteristic. In one example, the
light emitters corresponding to one wavelength band can be arranged
to surround one or more light emitters corresponding to another
wavelength band.
[0220] In a preferred form the housing can include means to
minimise ambient light arriving at the light sensitive element. For
example, the means can include one or more filters which attenuate
light outside the wavelength bands emitted by the light emitting
elements. Alternatively, it can include one or more baffles or
walls arranged within the housing such that the light sensitive
element is substantially shielded from receiving direct light from
outside the housing.
[0221] In a further aspect the present invention provides a method
of determining the output strength of a light emitting element of a
light source in a particle detector. The method including
illuminating the light emitting element in accordance with a
modulation pattern including "on periods" in which the light
emitter is emitting light and "off periods" in which no light is
emitted by the light emitter; detecting the output from the light
emitting element in one or more on periods and one or more off
periods; correcting the detected light output in one or more on
periods on the basis of the measured light level in the one or more
off periods. For example, the correction may including subtracting
the off period measurement from an adjacent on period measurement.
Alternatively, the on or off periods may be accumulated or averaged
over some predetermined number of corresponding on or off periods
to determine the light output level.
[0222] In another aspect the present invention provides a light
source for a particle detector including at least one light emitter
of a type described herein.
[0223] The light source can include a modulation circuit component
adapted to control an illumination pattern of the light source and
a feedback circuit component electrically connected to the light
sensitive element and adapted to receive an input therefrom and
output a control signal to the modulation circuit.
[0224] The modulation circuit can be adapted to vary one or more
of: [0225] the duration of illumination; [0226] the intensity of
illumination; [0227] the voltage applied to a light emitter; or
[0228] the current applied to a light emitter, [0229] on the basis
of a level of or variation in the received feedback signal
received.
[0230] In a further aspect, the present invention provides a method
in a light source of a particle detector, the method including:
illuminating at least light emitter of the light source according
to a first modulation pattern, the pattern including a plurality of
illumination pulses; receiving a feedback signal; adjusting the
modulation pattern in response to the feedback signal.
[0231] The method can include adjusting at least one of: [0232] the
duration of illumination; [0233] the intensity of illumination;
[0234] the voltage applied to a light emitter; [0235] the current
applied to a light emitter.
[0236] Preferably the feedback signal is generated by a light
sensitive element arranged to monitor the light output at least one
light emitting element of the light source.
[0237] The feedback signal can be a signal adapted to compensate
for a predetermined characteristic of at least one light emitter of
the light source. The predetermined characteristic can be a
temperature response of a light emitter.
[0238] In an embodiment of the present invention the step of
adjusting the modulation pattern in response to the feedback signal
can include adjusting the modulation pattern to encode data
relating to the output intensity of at least one light emitter of
the light source. For example, one or more modulation pulses may
be, inserted into, or adjusted in, the modulation pattern to
transmit light emitter output data to a receiver of the output of
light.
[0239] In another aspect of the present invention there is provided
a component for a beam detector including: [0240] a housing having
at least one side defining at least one internal volume, the at
least one wall including an optically transmissive wall portion
through which light may pass into or out of the housing; [0241] an
electro-optical system within the internal volume adapted to
transmit and/or receive light through an optically transmissive
wall portion of the housing; [0242] a foreign body detection system
adapted to detect a foreign body on or near an outer surface of the
optically transmissive wall portion, and including a light source
adapted to illuminate the outer surface and any foreign body on or
near the outer surface; [0243] a light receiver to receive light
scattered from the foreign body in the event one is illuminated,
and generate an output signal; [0244] a controller adapted to
analyse the output signal and apply fault logic to determine the
presence of a foreign body in the event that one or more criteria
are met and take an action.
[0245] The light receiver can be any one of: [0246] a photo diode;
and [0247] part of a light sensor array used to detect particles in
use.
[0248] The light source can be mounted within the internal volume.
Alternatively it can be mounted outside the housing.
[0249] In a first aspect the present invention provides a method,
in a particle detection system comprising one or more light sources
and a receiver arranged so that light from the one or more light
sources traverses an area to be monitored for particles and is
received by the receiver, and a controller programmed to monitor
for the occurrence of one or more predefined alarm and/or fault
conditions based on at least one received light intensity
threshold; the method including: providing at least one initial
light received intensity threshold for use by the controller during
a commissioning period; and providing at least one first
operational received light intensity threshold for use during an
operational period following the commissioning period.
[0250] Preferably a received light intensity threshold provided
during the commissioning period includes a minimum received light
intensity threshold, below which a fault condition may be
indicated.
[0251] The received light intensity threshold provided during the
operational period can include a minimum received light intensity
threshold, below which either a fault condition or alarm condition
may be indicated.
[0252] The minimum received light intensity threshold in the
commissioning period can be above a minimum received light
intensity threshold during at least a portion of the operational
period.
[0253] The method can further include: providing at least one
second operational light intensity threshold, after the passing of
a delay period, at least one second operational light intensity
threshold being for use during at least part of the operational
period following the delay period.
[0254] The second operational intensity threshold can be based on
one or more measurements of received intensity during the delay
period.
[0255] This second operational light intensity threshold is
preferably higher than at least one first operational light
intensity threshold. The second operational light intensity
threshold can be lower than at least one initial light intensity
threshold.
[0256] The method further include: determining the passing of the
delay period. The step of: determining the passing of the delay
period can be performed automatically by the controller; and/or
upon the receipt of an command signalling the end of the delay
period.
[0257] If the received light includes a plurality of wavelength
components the method includes: determining the occurrence of at
least one predefined alarm condition based on the received light
intensity at two or more wavelengths. The method can include,
determining the occurrence of one or more predefined alarm
conditions based on combination of the received light intensity at
two or more wavelengths.
[0258] The method can further include, initiating the operational
period after the commissioning period. Initiating the operational
period can be performed, automatically, e.g. based in a timer; or
upon the receipt of an initiation command.
[0259] In a further aspect the present invention provides a
controller for particle detection system comprising one or more
light sources and a receiver arranged so that light from the one or
more light sources traverses an area to be monitored for particles
and is received by the receiver, the controller being programmed to
monitor for the occurrence of one or more predefined alarm and/or
fault conditions based on at least one received light intensity
threshold; said controller being adapted to perform a method as
described herein.
[0260] The controller can initiate an action upon the occurrence of
one or more predefined alarm and/or fault conditions. For example
the action can be the generation of an alarm or error signal.
[0261] The present invention also provides a particle detection
system including such a controller. The particle detection system
can further includes, a receiver for receiving light; one or more
light sources arranged to emit light at one or more wavelengths, so
that light from the one or more light sources traverses an area to
be monitored for particles and is received by the receiver.
Preferably each light source is a light emitting diode. The
receiver can include an array of light sensor elements, e.g. the
receiver can be a video camera.
[0262] A further aspect of the present invention can also provide a
method of commissioning and operating a particle detection system,
comprising: arranging one or more light sources and a receiver so
that light from the one or more light sources traverses an area to
be monitored for smoke before being received by the receiver; and
performing the method which is an embodiment of the first aspect of
the present invention.
[0263] In a further aspect there is provided a particle detection
system for monitoring a volume, the system including: at least one
transmitter adapted to transmit one or more light beams; a receiver
adapted to receive said one or more light beams from at least one
transmitter after traversing the volume being monitored; a
controller adapted to determining the presence of particles in the
volume on the basis of the output of the receiver; and means for
determining a light output intensity of a transmitter for use in
particle detection.
[0264] The means for determining a light output intensity of the
transmitter are associated with the transmitter. The means for
determining a light output intensity of the transmitter can include
one or more filters selectively able to be selectively positioned
in a path of a beam of light emitted by the transmitter. The
transmitter can include mounting means configured to receive one or
more filter elements to enable the intensity of the light output by
the transmitter to be set to a determined level.
[0265] The means for determining a light output intensity of the
transmitter can include electronic control means adapted to
electronically control the light output of the transmitter. The
electronic control means can include one or more switches able to
be manually controlled to select the a light output intensity for
the transmitter.
[0266] The electronic control means may be in data communication
with a receiver and is adapted to receive control information from
the receiver relating to the received light level form the
transmitter, and is adapted to control the light output of the
transmitter in response to said control information.
[0267] The means for determining a light output intensity of a
transmitter for use in particle detection can be associated with
the receiver.
[0268] The transmitter can be adapted to transmit a plurality of
signals at different intensity levels. In this case the means for
determining a light output intensity of a transmitter for use in
particle detection can include, means associated with the receiver
to determine the received light intensity level for the at the
plurality of signals transmitted at different intensity levels and
compare the received light intensity level to one or more criterion
to determine the a light output intensity of the transmitter for
use in particle detection.
[0269] The transmitter can be adapted to transmit a repeated
pattern of signals including a plurality of signals at different
intensity levels; and the receiver can be adapted to selectively
receive the one or more signals in the repeated pattern determined
to be used in particle detection.
[0270] The transmitter may include means for generating a repeated
pattern of signals including a plurality of signals configured to
produce different received light levels at a receiver of the
detection system.
[0271] The particle detection system is most preferably a beam
detector.
[0272] The repeated pattern of signals can include signals
transmitted with different intensity levels. Te repeated pattern of
signals can include signals of different durations.
[0273] In another aspect the present invention provides a
transmitter for a particle detection system, including: at least
one light source to generate a beam of light at least one
wavelength; a housing in which the light source is mounted; one or
more filters selectively mountable with respect to the light source
for selectively attenuating the beam of light.
[0274] The transmitter can includes a power source to powering the
at least one light source.
[0275] The transmitter can includes control circuitry to control an
illumination pattern of the at least one light source.
[0276] In yet another aspect the present invention provides a
receiver for a particle detection system: at least one light sensor
for measuring the level of light received from a transmitter of a
particle detection system; a controller to selectively activate the
light sensor to receive signals. The controller can be adapted to
selectively activate the light sensor to predetermined receive
signals transmitted by a transmitter of a particle detection
system.
[0277] The predetermined signals transmitted by a transmitter can
be predetermined on the basis of the measured level of light
received by the sensor in an earlier time period.
[0278] The test filter comprising at least one sheet like filter
element, and being configured to transmit light in a first
wavelength band transmitted by the particle detector to a different
extent than light in a second wavelength band transmitted by the
particle detector. Preferably, the test filter transmits a light in
a shorter wavelength and emitted by the particle detector less than
it transmits light in a longer wavelength band transmitted by the
particle detector.
[0279] The test filter may include one or more sheets of filter
material.
[0280] In one embodiment, a sheet or sheets of filter material may
be formed of a material such that differential transmission at the
two wavelengths is achieved. Alternatively, one or more of the
filter elements can be treated or impregnated with colour selective
transmissive material. The material in this case can be a dye.
[0281] In a preferred form the test filter includes a plurality of
filter elements combined at such a manner to achieve predetermined
transmission characteristic. Preferably, the transmission
characteristics mimic smoke at a predetermined concentration. The
plurality of sheets can be combined in such a manner to provide a
selectable transmission characteristic.
[0282] In one embodiment, a sheet or sheets of substantially
transparent material to which has been added particles in a
predetermined size range corresponding to particles to be detected
by the detector under test. Most preferably, the particles are
between 0.2 and 1.0 micron in diameter.
[0283] In a further embodiment a filter element may have a surface
treatment to create a desired absorption characteristic. In one
form, a filter element can include a textured surface. The textured
surface can be caused by, for example, mechanical abrasion,
particle blasting, chemical or laser etching.
[0284] In an alternative embodiment, third form, surface is printed
with predetermined number of dots corresponding to the
predetermined transmission.
[0285] The filter elements may reflect or absorb light which is not
transmitted. However, absorption is typically more convenient.
[0286] In a first aspect present invention provides a receiver in a
particle detector, said receiver including at least one receiver
element adapted to receive light and output a signal indicative of
the received light intensity at plurality of spatial positions; and
an optical system including at least one wavelength selective
element configured to receive light at a plurality of wavelengths
simultaneously and transmit light in two or more wavelength bands
to the one or more sensor elements such that an output signal
indicative of the received light intensity in the at least two
wavelength bands can be obtained.
[0287] In a preferred form the receiver is configured to measure
the received light intensity at a plurality of spatially separate
positions in a plurality of wavelength bands substantially
simultaneously.
[0288] In one form of the invention, the wavelength selective
element can include a one or more filter elements placed in a light
path before the receiver. Most preferably, the filter element or
elements includes a mosaic dye filter. Alternatively, the
wavelength selective element can include one or more light
separating elements, e.g. prisms, diffraction gratings, or the
like. In a further alternative, the light separation element can be
combined with the light sensor element, and comprise a
multi-layered light sensitive element wherein respective layers of
the light sensitive element are configured to measure the intensity
of light in a corresponding wavelength band.
[0289] In a particularly preferred form, the wavelength bands of
interest include an infrared band and an ultraviolet band. In this
example, the wavelength selective elements can be adapted to be
infrared selective and ultraviolet selective.
[0290] In some embodiments of the present invention the wavelength
selective element may be adapted to split the incoming beam of
light into respective wavelength components and direct each
wavelength component to a corresponding sensor or subset of
elements of a sensor.
[0291] In a further aspect the present invention provides receiver
for a beam detector including filtering means having multiple
passbands. In one form, the filtering means can include a multiple
passband interference filter. For example, such a filter may be
arranged to selectively transmit in first passband sensor a long
wavelength and one or more harmonics of that wavelength. For
example, the filter can be designed to transmit substantially all
of the light at 800 nanometres and 400 nanometres while blocking a
large majority of light at other wavelengths. The filtering means
can include a plurality of filters. For example, the plurality of
filters can include more than one interference filter or plurality
of dye filters or the like. Said plurality filters can be arranged
in a predetermined spatial pattern such that light in different
passbands falls on different portions of a sensor of the
receiver.
[0292] In a further aspect of the present invention there is
provided a projected beam particle detector including a receiver of
the type described above. Preferably, the particle detector
includes a polychromatic light source. Most preferably, the light
source can be adapted to emit light in a plurality of wavelength
bands simultaneously. In a particularly preferred embodiment, the
light source includes synchronously operated monochromatic light
sources. However, it may alternatively include a polychromatic
light source. The polychromatic light source can include xenon
flash tube or krypton light source. Alternatively, the light
emitter may be a combination of a phosphorescent material and light
emitter arranged to illuminate the phosphorescent material. The
light emitter may, for example be an LED.
[0293] In a further aspect of the present invention there is
provided a transmitter for a beam detector including a light source
adapted to emit light in a plurality of wavelength bands
corresponding substantially to respective passbands of filter of
the receiver of the beam detector.
[0294] In a further aspect the present invention provides a beam
detector comprising at least one receiver and transmitter made in
accordance with the foregoing aspects of the invention.
[0295] According to one aspect of the invention, there is provided
a smoke detector including: [0296] a transmitter adapted to emit a
light beam; [0297] a receiver having a light sensor with a
plurality of sensor elements, for detecting the light beam, each of
the sensor elements being adapted to generate an electrical signal
related to the intensity of light impinging upon it; [0298] the
transmitter and received being arranged such that at least a
portion of a light beam from the transmitter is received by the
receiver; [0299] a beam diffusing optics located in a path of
travel of the light beam to the receiver, for forming a diffused
image of the light beam on the light sensor, and [0300] a
controller that processes electrical signals generated by a
plurality of the sensor elements to determine the intensity of the
received beam, and apply alarm and/or fault logic to the intensity
data to determine if a predetermined condition is fulfilled, and
initiate an action if the predetermined condition is fulfilled.
[0301] The beam diffusing optics can include a lens which focuses
the light beam at a point which is not coincident with the sensor.
The beam diffusing optics can optionally include a diffuser which
may be placed between the transmitter and the light sensors. A
diffuser and lens can be used together.
[0302] The diffused image of the beam preferably covers a plurality
of sensor elements on the sensor of the receiver. For example it
can cover between 2 and 100 elements. Preferably it covers between
4 and 20 sensor elements, although it may be more depending on the
size and density of sensor elements on the sensor. The diffused
image of the beam is preferably larger than a sharply focused image
of the beam would be.
[0303] The controller is preferably adapted to combine the received
signals from a plurality of sensor elements to determine the
received light level. In one form the measured light level from a
plurality of sensor elements are added. Prior to adding the signal
levels of each contributing sensor element can be weighted.
[0304] The controller may determine a centre-of-signal position
corresponding to an image of a beam on the light sensors, and
weight the signal from each sensor element according to a distance
between each sensor and the centre-of-signal position.
[0305] The transmitter may transmit a beam of light having
components in two or more wavelength bands.
[0306] According to another aspect of the invention, there is
provided a method for detecting smoke, including: [0307]
transmitting a light beam from a transmitter toward a receiver
having a sensor comprising multiple sensor elements; [0308]
arranging a receiver so that it receives the beam; [0309] forming a
diffused image of the light beam on the sensor; [0310] generating
electrical signals related to the intensity of the received light
level detected by at least those sensor elements of the multiple
sensor elements on which the beam impinges; [0311] determining the
intensity of the received beam based on a plurality of the signals;
[0312] applying an alarm and/or fault logic to the received
determined intensity; and [0313] initiating an action if a
predetermined alarm and/or fault condition is determined.
[0314] The step of forming a diffused image of the beam optionally
comprises defocusing the light beam such that it is focused at a
position that is not coincident with the light sensor.
[0315] Alternatively or additionally, the step of diffusing the
beam may include placing a diffuser between the transmitter and the
sensor.
[0316] The step of determining the intensity of the received beam
can include combining a plurality of the received signals. The
signals can be weighted in the combination. For example the method
can include determining a centre of signal position of the diffused
image of the beam and weighting the signals according to the
distance of their corresponding sensor element from the centre of
signal position.
[0317] In a first aspect the present invention provides a component
for a particle detection system including, a first processor
adapted to intermittently receive data from an image capture device
and to process said data; a second processor communicatively
coupled with the first processor and adapted to selectively
activate the first processor.
[0318] The second processing device can be additionally configured
to perform one or more of the following additional functions of the
particle detection system, communication with an external data
communication system connected to the particle detector; control of
one or more interface components of the system; monitoring of a
fault condition of the component, or the like.
[0319] Preferably the second processor is of lower power
consumption than the first processor.
[0320] The component preferably also includes imaging means to
receive one or more optical signals from a transmitter associated
with the particle detection system.
[0321] In a second aspect of the present invention there is
provided a method in a particle detection system. The method
includes, monitoring an activation period of a first processor
using a second processor; activating the first processor in
response to a signal from the second processor; and performing one
or more data processing steps with the first processor.
[0322] The method can include deactivating the first processor upon
completion of one or more processing tasks.
[0323] The first processor is preferably adapted to process video
data from a receiver of the particle detection system.
[0324] In one aspect the present invention provides a light source
for a particle detector, including: [0325] at least one light
emitter for emitting at least one beam of light for illuminating a
part of a region being monitored; [0326] a battery for supplying
electrical power to the light source; [0327] a battery monitor for
measuring at least one of the voltage of the battery or its current
output; [0328] a controller configured to, control the illumination
of at least one light emitter of the light source and to receive at
least one of, the voltage of the battery or its current output, and
to determine a valve indicative of a remaining expected battery
life. Preferably, the controller is adapted, in the event that the
remaining expected battery life is less than a predetermined period
of time, to generate an indication of the remaining expected
battery life.
[0329] Preferably the light source includes an environmental
monitor to monitor an environmental factor affecting the remaining
expected battery life, e.g. temperature.
[0330] The predetermined period of time is preferably longer than a
period between scheduled, recommended or mandated servicing
intervals for the light source.
[0331] In another aspect the present invention provides
environmental monitoring system including: [0332] a beam detector
subsystem including at least one transmitter adapted to emit one or
more beams of light across a region being monitored and at least
one receiver, adapted to receive at least one beam of light emitted
by a transmitter; [0333] at least one additional environmental
monitor adapted to sense an environmental condition associated with
the region being monitored and to communicate an output, via an
optical communication channel, to a receiver of the beam detector
subsystem.
[0334] In a preferred form, the optical communications channel can
be implemented by modulating a beam output by one or more
transmitters of the beam detection subsystem.
[0335] Alternatively, the optical communications channel can
include a light emitter associated with the one or more additional
environmental monitors and arranged to lie within a field of view
of a receiver of the beam detector subsystem wherein the light
emitter is adapted to be modulated to communicate a sensed
condition by an associated environmental monitor.
[0336] In a particularly preferred form the light receiver of the
beam detector subsystem can include one or more sensors including a
plurality of sensing elements adapted to measure a received light
intensity at a plurality of spatial positions. Such a system can be
used to simultaneously monitor an optical communications channel
and a particle detection beam of one or more transmitters of the
beam detector subsystem.
[0337] In a further aspect of the present invention there is
provided the beam detection system comprising a plurality of beam
detectors; at least one controller in data communication with the
detectors and receiving an output from each of said beam detectors.
The controller being adapted to correlate the output of at least a
pair of beam detectors which are spatially substantially spatially
coincident for at least part of their beam length and in the event
that a predetermined correlation condition exists determining that
either particle detection event or a fault condition has occurred.
In one form, the correlation includes a temporal correlation. The
correlation may include a particle detection level correlation. In
a simple form, the correlation may simply be performed by comparing
whether the particle detection level of two or more beam detectors
are substantially equal, alternatively, a particle detection
profile for a plurality of beam detectors may be compared to one
another to determine the extent of correlation between them.
[0338] In another aspect of the present invention there is provided
a method of operating a particle detection system including
plurality of beam detectors having beams that can substantially
coincident at least one point. The method including receiving an
output from the plurality of beam detectors, determining if a
correlation condition exists between at least two of the outputs,
and if a predetermined correlation condition exists; determining
either a particle detection event or false alarm event has occurred
according to predetermined particle detection and/or fault logic.
The alarm can include cross correlating a time varying particle
detection profile of two detectors. It can also or alternatively
include determining a correlation between a particle detection
state i.e. an alarm level or alarm threshold crossing of the two or
more detectors.
[0339] Throughout this specification the term "beam" will be used
in reference to the output of a light emitter such as an LED. The
beam will not necessarily be collimated or confined to a single
direction, but may be divergent, convergent or of any suitable
shape. Similarly, "light" should be understood to broadly mean
electromagnetic radiation and is not confined to the visible
portion of the electromagnetic spectrum.
[0340] In another aspect the present invention provides a particle
detection system including; at least one light source adapted to
illuminate a volume being monitored, said illumination including a
pulse train including a plurality of pulses, said pulse train being
repeated with a first period; a receiver having a field of view and
being adapted to receive light from at least one light source after
said light has traversed the volume being monitored and being
adapted to generate signals indicative of the intensity of light
received at regions within the field of view of the receiver, said
receiver being configured to receive light from the at least one
light source in a series defined by an exposure time and receiving
frame rate; a processor associated with the receiver adapted to
process the signals generated by the receiver, wherein the pulses
with the pulse train emitted within each plurality of pulses has a
temporal position that is related to the receiving frame rate.
[0341] A pulse in the pulse train can preferably have a duration
about half the exposure time. Preferably the period of repetition
of the pulse train is substantially longer than the period between
temporally adjacent frames. The frame rate is in any one of the
following ranges: 100 fps-1500 fps, 900 fps-1100 fps, 500 fps to
1200 fps. Most preferably the frame rate is about 1000 fps.
[0342] The duration of a pulse is preferably between 1 .mu.s and
100 .mu.s. Most preferably the duration of a pulse is about 50
.mu.s.
[0343] The exposure time will typically be between 2 and 200 .mu.s.
Preferably the exposure time is about 100 .mu.s.
[0344] The pulse train can include at least one synchronisation
pulse. Preferably it includes 2. The pulse train can include at
least one pulse at a first wavelength. the pulse train can include
at least one pulse at a second wavelength. The pulse train can
include at least one data pulse.
[0345] The frame rate and temporal spacing between each of the
pulses are selected such that, in at least a first time period,
there is changing phase difference between them. the frame rate and
temporal spacing between each of the pulses are selected the
temporal spacing between each of the pulses is such that each of
the pulses in a pulse train substantially fall within a respective
exposure.
[0346] In another aspect of the present invention there is provided
a method in a particle detection system including; at least one
light source adapted to illuminate a volume being monitored, a
receiver having a field of view and being adapted to receive light
from at least one light source after said light has traversed the
volume being monitored and being adapted to generate a series of
frames indicative of the intensity of light received at regions
within the field of view of the receiver, and a processor
associated with the receiver adapted to process the signals
generated by the receiver, and provide an output; said method
including: determining a number of light sources from which the
receiver is receiving light.
[0347] The method can further include: analysing a plurality of
frames output by the receiver to determine the number of light
sources.
[0348] The method can further include: operating the receiver at a
high frame rate during the step of determining the number of light
sources; and subsequently operating the receiver at a second lower
frame rate.
[0349] The method can further include: analysing a plurality of
frames from the receiver to identify regions having relatively high
variation in received light level between frames to identify
candidate positions within the field of view of the receiver.
[0350] The method can further include: comparing the variation in
received light levels for a position between frames to a
threshold.
[0351] The method can further include: attempting to synchronise
the receiver to a predetermined transmission pattern expected from
a transmitter for a candidate position, and in the event
synchronisation is successful determining the candidate position is
receiving light from a transmitter.
[0352] The method can further include: attempting to synchronise
the receiver to a predetermined transmission pattern expected from
a transmitter for a candidate position, and in the event
synchronisation is unsuccessful determining the candidate position
is not receiving light from a transmitter.
[0353] The step of attempting to synchronise the receiver to a
predetermined transmission pattern can include: capturing a
plurality of at least partial frames including the candidate
location; comparing the received frames to an expected pattern of
received light corresponding to a pulse train emitted by a
transmitter; attempting to synchronise to the received pattern
using a phase locked loop.
[0354] The step of comparing the received frames to an expected
pattern of received light corresponding to a pulse train emitted by
a transmitter; can include determining a reference level of
received light representing a time when no pulse is received for
the candidate position; comparing a light level received from each
pulse to the reference level and if the difference exceeds a
predetermined threshold, determining a pulse is received.
[0355] The step of comparing the received frames to an expected
pattern of received light corresponding to a pulse train emitted by
a transmitter; can includes determining whether a series of pulses
corresponding to an expected pattern is received.
[0356] The method can further include: comparing the determined
number of light sources with a predetermined number of light
sources; and in the event that the determined number does not match
the predetermined number either: repeating the determining step; or
signalling a fault.
[0357] In order to more clearly explain each of the aspects of the
present invention and their implementation, these aspects have each
been described in relation to separate embodiments. A person
skilled in the art will readily understand how to combine two or
more of such embodiments into an implementation of the invention.
Thus it should be understood that the invention disclosed and
defined in this specification extends to all alternative
combinations of two or more of the individual features and aspects
mentioned or evident from the text or drawings. All of these
different combinations constitute various alternative aspects of
the invention.
[0358] Throughout this specification the term "beam" will be used
in reference to the output of a light emitter such as an LED. The
beam will not necessarily be collimated or confined to a single
direction, but may be divergent, convergent or of any suitable
shape. Similarly, "light" should be understood to broadly mean
electromagnetic radiation and is not confined to the visible
portion of the electromagnetic spectrum.
[0359] As used herein, except where the context requires otherwise,
the term `comprise` and variations of the term, such as
`comprising`, `comprises` and `comprised`, are not intended to
exclude further additives, components, integers or steps.
BRIEF DESCRIPTION OF THE DRAWINGS
[0360] Illustrative embodiments of the present invention will now
be described, by way of non-limiting example only, with reference
to the accompanying drawings, in which:
[0361] FIG. 1 illustrates a conventional beam detector;
[0362] FIG. 2 illustrates a beam detector capable of implementing
an embodiment of the present invention;
[0363] FIG. 3 illustrates a beam detector capable of implementing
an embodiment of the present invention;
[0364] FIG. 4 illustrates a scenario in which a reflection may be
caused in a beam detector;
[0365] FIG. 5 illustrates a close-up view of a receiver in a beam
detector made in accordance with an embodiment of the present
invention;
[0366] FIG. 6 illustrates a beam detector set-up made in accordance
with another embodiment of the present invention;
[0367] FIG. 7 illustrates beam detector arrangement made in
accordance with another embodiment of the present invention;
[0368] FIG. 8 illustrates another embodiment of the beam detector
made in accordance with the present invention;
[0369] FIG. 9 illustrates schematically an embodiment of the
present invention in which the polarisation state of the
transmitter and receiver are aligned;
[0370] FIG. 10 illustrates schematically an embodiment of the
present invention with orthogonally arranged polarisation states at
the transmitter and receiver;
[0371] FIG. 11 illustrates an embodiment of the present invention
in which two orthogonally polarised beams are transmitted to a
polarisation sensitive receiver;
[0372] FIG. 12 illustrates an embodiment of the present invention
with a transmitter emitting a single polarised beam to be received
by two orthogonally polarised receivers;
[0373] FIG. 13 illustrates a plan view of a volume monitored by a
particle detection system operating according to an embodiment of
the present invention;
[0374] FIG. 14 illustrates a cross sectional view through a volume
of FIG. 13 showing the receiver and one transmitter of that
system;
[0375] FIG. 15 illustrates a schematic view of a receiver used in
an example of the embodiment of the present invention;
[0376] FIG. 16 shows a schematic representation of a transmitter
used in an embodiment of the present invention;
[0377] FIG. 17 shows diagrammatically a smoke detector and mounting
arrangement according to the invention;
[0378] FIG. 18 shows a cross sectional side view of the smoke
detector shown in FIG. 17;
[0379] FIG. 19 shows a side view of another embodiment of smoke
detector apparatus according to the invention;
[0380] FIG. 20 shows a plan view of another embodiment of smoke
detector apparatus according to the invention;
[0381] FIG. 21 shows a diagrammatic illustration of a further
embodiment of smoke detector apparatus according to the
invention;
[0382] FIG. 22 shows a cross sectional view through a component of
a smoke detector made in accordance with an alternative embodiment
of the present invention;
[0383] FIG. 23 is a schematic diagram of a beam-detector assembly
having a first module and a second module, the assembly being
powered up when the two modules are assembled;
[0384] FIG. 24 is a perspective view of a transmitter, in
accordance with an embodiment of the present invention;
[0385] FIG. 25 is a close up perspective view of the brake shoe and
spindle of the transmitter of FIG. 24;
[0386] FIG. 26 is a perspective cutaway view of the receiver of
FIG. 24;
[0387] FIG. 27 is a perspective view of a receiver in accordance
with an embodiment of the present invention;
[0388] FIG. 28 is a close up perspective view of the brake shoe,
lever arm and spindle of the transmitter of FIG. 27;
[0389] FIG. 29 illustrates a plot of received light at two
wavelengths in a beam detector according to an embodiment of the
present invention;
[0390] FIG. 30 shows a plot of the gain and corrected output when
implementing a method according to an embodiment of the present
invention;
[0391] FIG. 31 shows the received light level in two wavelength
bands in an embodiment of the present invention; and
[0392] FIG. 32 shows the corrected output level and adjusted gain
levels when implementing methods according to an embodiment of the
present invention in the conditions described in FIG. 31.
[0393] FIG. 33 illustrates a particle detection system
incorporating a light source in accordance with an embodiment of
the invention;
[0394] FIG. 34 illustrates the light source of FIG. 33 when
partially obstructed by a foreign body;
[0395] FIG. 35 illustrates the light source of FIG. 33 when
obstructed by smoke;
[0396] FIG. 36 illustrates an alternative embodiment of the light
source depicted in FIGS. 33 to 35;
[0397] FIG. 37 illustrates a particle detection system
incorporating a light source in accordance with an alternative
embodiment of the invention;
[0398] FIG. 38 illustrates the light source of FIG. 37 when
partially obstructed by a foreign body;
[0399] FIG. 39 illustrates an alternative embodiment of the light
source depicted in FIGS. 37 and 38;
[0400] FIG. 40 illustrates an optical subsystem usable in an
embodiment of the present invention;
[0401] FIGS. 41 and 42 illustrate light sources in accordance with
further embodiments of the invention;
[0402] FIGS. 43 and 44 illustrate the effect of modifying the beam
width of a light source used in a particle detection system;
and
[0403] FIGS. 45 and 46 illustrate an advantage of having different
spatial profiles for light in different wavelength bands of emitted
light used in a particle detection system;
[0404] FIG. 47 illustrates a light emitter usable in a first
embodiment of the present invention;
[0405] FIG. 48 illustrates further detail of light emitter usable
in an embodiment of the present invention;
[0406] FIG. 49 illustrates a further embodiment of a light emitter
usable in an embodiment of the present invention;
[0407] FIG. 50 is a schematic block diagram illustrating a circuit
usable in an embodiment of the present invention;
[0408] FIG. 51 is a plot illustrating the operation of the circuit
of FIG. 50;
[0409] FIG. 52 is a schematic block diagram illustrating a second
circuit usable in an embodiment of the present invention;
[0410] FIG. 53 is a plot illustrating the operation of the circuit
of FIG. 52.
[0411] FIG. 54 illustrates a schematic representation of a light
source of a beam detector employing an embodiment of the present
invention;
[0412] FIG. 55 illustrates a schematic representation of a light
source of a beam detector employing an embodiment of the present
invention;
[0413] FIG. 56 illustrates a schematic representation of a light
source of a beam detector employing an embodiment of the present
invention.
[0414] FIG. 57 illustrates a room in which a particle detection
system according to an embodiment of the present invention is
installed;
[0415] FIG. 58 shows a flow chart of one embodiment of process that
may be implemented to install a beam detector operating in
accordance with an embodiment of the present invention.
[0416] FIG. 59 shows a flow chart of one embodiment of a process
that may be performed by a controller of a beam detector according
to an embodiment of the present invention after installation;
[0417] FIG. 60 shows a flow chart of another embodiment of a
process that may be performed by a controller of a beam detector
according to an embodiment of the present invention following
installation;
[0418] FIG. 61 illustrates schematically part of a transmitter
according to an embodiment of the present invention;
[0419] FIG. 62 shows a second embodiment of the transmitter
illustrated in FIG. 61;
[0420] FIG. 63 illustrates exemplary attenuators able to be used
with an embodiment of the present invention;
[0421] FIG. 64 is a timing diagram illustrating graph of
transmission power and corresponding receiver state illustrating
another embodiment of the present invention;
[0422] FIG. 65 illustrates schematically a particle detection
system employing a test filter in accordance with an aspect of the
present invention;
[0423] FIG. 66 illustrates an exemplary test filter made in
accordance with an embodiment of the present invention;
[0424] FIG. 67 is a plot of the transmission spectrum of a filter
made in accordance with an embodiment of the present invention;
[0425] FIG. 68 to FIG. 75 illustrates various embodiments of
filters made in accordance with an aspect of the present
invention.
[0426] FIG. 76 illustrates schematically a particle detection
system made in accordance with an embodiment of the present
invention;
[0427] FIG. 77 illustrates an exemplary receiver made in accordance
with an embodiment of the present invention;
[0428] FIG. 78 illustrates a further illustrative embodiment of a
light receiver according to the present invention;
[0429] FIG. 79 illustrates a further light receiver made in
accordance with an embodiment of the present invention;
[0430] FIG. 80 illustrates a fourth embodiment of the light
receiver made in accordance with an embodiment of the present
invention.
[0431] FIG. 81 is a schematic representation of a beam detector
that utilises an embodiment of the present invention;
[0432] FIG. 82 is a schematic representation of the beam detector
represented in FIG. 81, showing a different transmitter
position;
[0433] FIG. 83 is a schematic diagram depicting one embodiment of a
diffusing means, of an embodiment of the present invention where
the transmitter is sufficiently far away that the beam rays
entering the lens are essentially parallel;
[0434] FIG. 84 is a schematic diagram depicting another embodiment
of the diffusing means of the present invention;
[0435] FIG. 85 illustrates a further embodiment of an aspect of the
present invention;
[0436] FIGS. 86 through 89 illustrate multiple wavelength filter
arrangements which are able to be used in an embodiment of the
present invention, such as that illustrated in FIG. 85.
[0437] FIG. 90 is a schematic illustration of a fire alarm system
which may be adapted to operate in accordance with an embodiment of
the present invention;
[0438] FIG. 91 illustrates a schematic block diagram of a receiver
component of beam detector according to an embodiment of the
present invention; and
[0439] FIG. 92 illustrates an exemplary pulse train used in an
embodiment of the present invention.
[0440] FIG. 93 illustrates schematically an environmental
monitoring system in accordance with a first embodiment of the
present invention;
[0441] FIG. 94 illustrates a second embodiment of an environmental
monitoring system in accordance with a second embodiment of the
present invention;
[0442] FIG. 95 illustrates schematically a light source able to be
used in an embodiment of the present invention;
[0443] FIG. 96 illustrates a system made in accordance with a
further embodiment of the present invention.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0444] FIG. 4 illustrates a beam detector of the type described
above. The beam detector 100 includes a transmitter 102 and a
receiver 104. The beam detector 100 is set-up to detect particles
in a volume 101, which may be a room for example. The transmitter
102 emits a diverging beam of light over a field of illumination
defined by lines 106. The beam of light includes a direct
illumination path 108 which arrives without reflection at the
receiver 104. Within the field of illumination 106 of the
transmitter 102 some rays will arrive at the receiver 104 by a
reflected path, e.g. path 110 which reflects off the ceiling 112
defining the volume 101. The present inventors have determined that
if certain conditions are fulfilled, the presence of the reflected
beam 110 can be ignored. For example, if the received beam
satisfies minimum received intensity requirements; and, in the
event that the beam includes distinguishable characteristics, e.g.
wavelength components and/or polarisation states, that the received
beam possesses the predetermined characteristics. In some cases it
is relevant whether the beam which is used for detecting particles
is the direct beam 108 or the reflected beam 110, for example, in a
multiple wavelength system, it may be that the surface finish of
the ceiling 112 is such that light in one wavelength band will be
reflected more completely than light in a second wavelength band.
In the event that these wavelength bands coincide with wavelength
bands transmitted by the transmitter 102 that are used for particle
detection by the receiver 104, a differential measure of received
light intensity in the two wavelength bands will behave differently
in the reflected light path 110 than in the direct light path 108.
Accordingly, in this case, it is necessary to correctly identify
the direct light path beam 108.
[0445] FIG. 5 illustrates one mechanism for determining a direct
beam from a reflected beam in such a system. In FIG. 5
corresponding features will be numbered with the same reference
numerals as FIG. 4. FIG. 5 illustrates a close-up view of the
receiver 104 of the beam detector 100 showing a reflected beam 110
and a direct beam 108. FIG. 5 also shows the detail of the sensor
200 of receiver 104. In this embodiment, the likelihood of
distinguishing the direct beam 110 from the reflected beam 110 is
improved by providing the light receiver 104 with a sensor having a
high spatial resolution. As described above, the sensor 200 of the
receiver 104 includes a multiplicity of sensing elements 202 which
can independently detect received light intensity at distinct
spatial positions. In FIG. 5, by providing a high resolution sensor
200 it can be seen that a group of pixel 208 are illuminated by a
direct beam 108 and a separate and distinct group of sensor
elements 210 are illuminated by the received reflected beam 110. If
the sensor element size was substantially larger it would not be
possible to resolve these two received beams into distinct groups
of sensor elements. In a particularly preferred form, the spatial
resolution of the light sensor is particularly high in the
direction of a plane defined by the direct beam and the reflected
beam.
[0446] In most embodiments the controller of the beam detector can
be configured to determine which of the spots, e.g. 210 or 208 has
the highest intensity, and to use the highest intensity beam for
particle detection. Typically, the brightest received beam will
correspond to the direct ray 108. In an extreme case, there may be
no sufficient discernable difference between intensity of the two
received light beams. In this case, the beam which arrives at the
receiver furthest from the reflecting surface is preferably
selected as the direct beam as the other beam i.e. a beam nearer
the reflective surface, is more likely to be the reflected ray.
[0447] In one exemplary embodiment, the resolution of the image
sensor is 640.times.480 pixels.
[0448] FIG. 6 shows a further beam detector installation made in
accordance with an embodiment of the present invention. In this
case, beam detector 300 includes a transmitter 302 and a receiver
304. The operation of the beam detector is substantially identical
to those described elsewhere herein. However, the beam detector
installation additionally includes two baffles 306 and 308 attached
to the reflecting surface 310. The baffles 306 and 308 extend
outwardly from the reflecting surface 310 towards the direct beam
path 312 and serve to intercept reflected beam paths which could
potentially reach the receiver 304. The number and length of the
baffles can be chosen to suit the particular installation and may
be positioned to extend almost entirely down to the direct beam
312. Alternatively, if accurate positioning is possible, a
relatively short baffle can be used if an accurate position of the
reflected beam can be determined. Another option involves a longer
baffle having an aperture accurately positioned so that the direct
beam 312 passes therethrough. As will be appreciated, the same
effect can be achieved by placing the transmitter and receiver in
close proximity to an existing structure which will act like a
baffle, for example, in a warehouse type installation in which the
warehouse has a number of horizontally extending ceiling support
beams placed beneath the ceiling, the transmitter receiver may be
located slightly below the beams such that the beams in effect
operate as baffles to prevent interference from reflections off the
ceiling's surface.
[0449] FIG. 7 illustrates a further embodiment of the present
invention. This embodiment shows a beam detector set-up 350
comprising a transmitter 354 and a receiver 356. The transmitter
352 emits a beam or beams of light over a predetermined
illumination field and as discussed with the previous embodiments,
both direct beams 358 and reflected beams 360 may arrive at the
receiver 356. In this embodiment, the receiver is configured such
that it has a field of view 8 that is relatively narrow in the
direction of the reflection and as such the receiver 356 is unable
to `see` the reflecting surface 362. If the receiver 356 cannot see
the reflective surface 362, the only light path to the receiver
from the transmitter 354 which will produce a sufficiently strong
signal to be discernable will be the direct beam 358. Similarly,
the field of illumination of the transmitter 354 can be confined
such that it does not illuminate the reflective surface 362.
Typically in beam detector installations the reflective surface
will be a ceiling of a room being monitored. In this case, the
field of view of the receiver 356 and/or the field of illumination
of the transmitter 354 will need to be constrained in the vertical
direction. Suitable fields of view for field of illumination will
have an angle of divergence of between 0.degree. and 5.degree..
However, this requirement will differ depending on the geometry of
the system. Clearly a system with a long distance, say a 100 metres
between the transmitter and the receiver will require a very narrow
angle of beam divergence or viewing angle to achieve this outcome.
However, in an embodiment with only 3 metres between the
transmitter and the receiver a much wider angle of illumination and
field of view is acceptable. Proximity to the reflective surface
will also influence the required angles to achieve the
aforementioned results.
[0450] FIG. 8 shows a further embodiment of a beam detector made in
accordance with an aspect of the present invention. In this
embodiment, the beam detector 500 includes a transmitter 502 and a
receiver 504. The transmitter 502 includes two light emitters 502A
and 502B. Each light emitter 502A, 502B emits a beam or beams of
light over its respective field of illumination and may direct a
direct beam 508 and a reflected beam 510 which arrive at the
receiver 504. The two light emitters 502A and 502B are configured
to be actuated in predetermined illumination sequence such that the
source of a received beam, i.e. which emitter it came from, can be
determined by analysing the light received at the receiver 504. In
this embodiment, the light which arrives at the receiver 504 via
the direct light path 508 will form an image 514A on the receiver
sensor (not shown), whereas the light received at the receiver by
the reflected light path 510 will form an image on the sensor of
the receiver 504 such as that shown at 514B. As will be
appreciated, the image formed on the receiver in the two cases
(i.e. direct and reflected) differ from each other in that one is a
mirror image of the other. The directly formed image 514A preserves
the relative positioning of the two light sources 502A and 502B
whereas, in the reflected image 514B, the positions of these two
sources 502A and 502B are flipped in the plane containing the
reflected beam and receiver. Accordingly, by analysing the received
images, it is possible to determine which pair of received beams
corresponds to the direct beam path 508 and which pair correspond
to the reflected beam path 510. In other embodiments of the present
invention the two light sources 502A and 502B can be light emitters
with different wavelength or polarisation characteristics, rather
than being illuminated with different modulation patterns.
[0451] As will be appreciated by those skilled in the art any
shaped arrangement of light images on the transmitter. For example,
a two dimensional ray of distinguishable light emitters can be
incorporated into a transmitter to allow determination of the
direct or reflected beams from any reflective surface in any
orientation with respect to the beam.
[0452] Turning now to FIG. 9, a beam detection system 1100 is
illustrated. The beam detection system can be of any of the types
described above and includes a transmitter 1102 and a receiver
1104. The transmitter can emit any number of beams of light in any
one or more transmission bands. The beam or beams emitted by the
transmitter 1102 are received by the receiver 1104. In this
embodiment, the transmitter is arranged to transmit polarised light
(e.g. vertically polarised light). The receiver 1104 is adapted to
receive only light having the same polarisation as that
transmitted.
[0453] Polarisation of the transmitter can be achieved in a wide
variety of ways including by using an inherently polarised light
source such as a laser diode or by placing a polarising filter in
the beam path of a randomly (or otherwise) polarised light source.
Similarly, the polarisation sensitivity of the receiver can be
determined by the inherent characteristics of the receiver or by
the placement of one or more polarising filters before the sensor
elements of the receiver.
[0454] In this example, nuisance light such as ambient sunlight
which is generally not polarised or is randomly polarised will be
substantially rejected by the receiver, whereas all of the
transmitted beam (less that proportion extinguished by particles
and objects between the transmitter and receiver) will be received
by the receiver 104.
[0455] FIG. 10 illustrates a similar system to the FIG. 9. The
system 1200 in FIG. 10 includes a transmitter 1202 which emits a
light beam 1206 that is received by the receiver 1204. In this
example, the transmitter is polarised in a first direction (e.g.
vertically polarised) and emits at least one polarised beam 1206.
The receiver 1204 is arranged to receive light in a polarisation
orthogonal to beam transmitted by the transmitter 1202. In this
case, the receiver 1204 is adapted to receive horizontally
polarised light. Such a polarisation offset presents a benefit in
that large particles, like dust, in the path of the beam 1206 may
be distinguished from small particles, like smoke. This is because
large particles like dust tend to forward scatter light with random
polarisation and thus increase the cross-polarised component of
light received at the receiver 1204.
[0456] Combinations of the two embodiments described in FIGS. 9 and
10 can be incorporated into a particle detection system. Turning
firstly to FIG. 11 the system 1300 includes a transmitter 1302 and
a receiver 1304. The transmitter 1302 is adapted to emit light
beams 1306A and 1306B. A first of these two light beams 1306A is
arranged to be emitted with a first polarisation state whereas the
second beam 1306B is emitted with an orthogonal polarisation state.
The receiver 1304 is arranged to receive light in a single
polarisation only e.g. in the first polarisation state.
Accordingly, as will be appreciated both techniques described in
relation to FIGS. 9 and 10 may be applied in the same receiver.
Preferably, the transmitter 1302 is arranged to generate beams
1306A and 1306B alternately so that the two polarisation state
beams arrive at different times at the receiver 1304.
[0457] An alternate system is illustrated in FIG. 12. In this
system the beam detector 1400 comprising a transmitter 1402 and a
receiver 1404. The transmitter 1402 is configured to emit a
vertically polarised beam 1406. The receiver 1404 is adapted to be
able to resolve light received in plurality of polarisation states
e.g. in vertical polarisation state or a horizontal polarisation
state. This can be achieved by having a plurality of adjacent light
receiving elements having different polarisations which are
operated either concurrently or alternately. In this example, a
beam splitting component 1408 is provided prior to the receiver
elements to direct beams to each of the receivers.
[0458] As will be appreciated by those skilled in the art
references the specification to vertical and horizontal
polarisation have been selected for convenience only and any
polarisations may be used. Moreover, for convenience of description
orthogonal polarisation states have been selected to illustrate the
present invention. However, the present invention should not be
taken as being limited to polarisation states which are either
aligned or orthogonal to one another. Other angular offsets between
polarisations are possible. Those skilled in the art will be able
to determine the appropriate calculations to perform to account for
this variation.
[0459] One way of achieving variation in polarisation states for a
receiver or transmitter is to provide mechanical means for placing
polarising filters in the light path. For example, a solenoid can
be used as an actuator to move a reciprocating polarising filter
into and out of the beam path. Alternatively a rotating filter
mechanism can be employed which has plurality of differently
polarised filters around a wheel like structure. By rotating the
wheel like structure through the light path different polarisations
can be achieved over time. Other mechanical arrangements are also
possible, for example, the light emitting element of the
transmitter 402 could be physically rotated about an axis as could
the one or more sensors of the receiver. Other mechanical
arrangements will be apparent to those skilled in the art.
[0460] FIG. 13 illustrates a plan view of a room 400A in which is
installed a beam detector system 402A according to an embodiment of
the present invention. The beam detection system includes a single
receiver 404A configured to monitor eight transmitters 406A, 406B
through 406H. Each of the transmitters 406A to 406H is adapted to
transmit light with a horizontal angle of illumination of a
degrees. It is also adapted to transmit light with a vertical angle
of illumination of .beta. degrees as show in FIG. 14. Similarly the
field of view of the receiver 404A differs in its horizontal and
vertical extent. In this example, the receiver 404A is adapted to
receive light over a viewing angle of .gamma. degrees and vertical
viewing angle of .delta. degrees. In a preferred form of the
present invention the horizontal angle of illumination of the
transmitters 406A to 406H is wider than their vertical angle of
illumination .beta.. Similarly, the receiver 404 has a wider
horizontal field of view than it does vertical field of view.
[0461] The differential fields of view and fields of illumination
of the receiver and transmitter respectively are chosen to account
for alignment tolerances in the typical installation. For example,
in most installations such as that illustrated in FIG. 13 the
transmitters 406A through 406H will typically be installed at the
same height as each other and the receiver 404A will be mounted in
a plane parallel to the transmitters 406A to 406H. Accordingly,
when the image of the transmitters 406A through 406H is received on
the light sensor of the receiver 404A they will tend to align on
the light sensor. Accordingly, a relatively narrow field of view
can be tolerated in the vertical direction for the receiver 404A.
However, as will be apparent from FIG. 4 a very wide horizontal
field of view is required by the receiver 404A. Similarly,
horizontal alignment of the transmitters 406A to 406H is more
difficult to achieve than vertical alignment in most installations.
This is typically because the range of movement in the vertical
plane is more limited and typically walls of a building are
relatively parallel in alignment. For this reason an installer may
get away with mounting the transmitter and receiver such that their
field of view is orthogonal to the plane of the surface on which
they are mounted and this will achieve a suitably accurate vertical
alignment. However, this may not be the case with horizontal
alignment as the angle of illumination of the light sources and
angle of reception of the light receiver will vary from the
orientation of the surface on which they are mounted due to the
geometry of the system being installed. Thus providing an ability
for horizontal alignment is necessary and the horizontal field of
view of the receiver and horizontal beam width of the transmitters
is advantageously relatively wide.
[0462] For example, a receiver may be adapted such that its
horizontal field of view approaches 90 degrees while its vertical
field of view is only around 10 degrees. Similarly, a transmitter
may be configured such that its horizontal beam width is around 10
degrees whereas its vertical beam width may be between 3 and 5
degrees.
[0463] In order to achieve different horizontal and vertical beam
divergences or viewing angles either a transmitter or receiver may
be fitted with an optical system including an anamorphic lens.
[0464] FIG. 15 illustrates an exemplary configuration of a receiver
such as that described in connection with FIG. 13.
[0465] The receiver 420 includes a multi segment light sensor 422
which is coupled to a video readout and processing subsystem 424.
The light receiver 920 includes an optical arrangement 426
comprising e.g. a plurality of lenses or other optical components
e.g. mirrors, for focusing received light on the sensor array 422.
In a preferred form, the anamorphic lens is arranged to provide a
substantially different horizontal and vertical field of view for
the receiver.
[0466] FIG. 16 illustrates a transmitter 700 which includes at
least one light emitter 702 adapted to emit one or more beams of
light in one or more wavelength bands. The transmitter 700 includes
control circuitry 704 which is powered by a power source 706 which
may, for example be a battery. The light emitter 702 emits a beam
of light 708. This beam of light is shaped into a particular
dispersion pattern or beam shape by an optical arrangement 710. As
described above, the optical arrangement 710 can include one or
more anamorphic lenses.
[0467] As will be appreciated by those skilled in the art different
installations will have different geometrical limitations placed on
them and requirements. Accordingly, the present invention should
not be considered as being limited to the case where the beam shape
of a transmitter e.g. 406 or a receiver e.g. 404 is defined by its
vertical or horizontal angles. Rather, the present invention
extends to systems in which either or both of the beam width of a
transmitter or angular extent of a receiver is different in any two
directions whether they are orthogonal with each other or not and
whether they are aligned vertically and horizontally or not.
[0468] Irrespective of whether the particle detection system is of
the type depicted in FIG. 1, FIG. 2 or FIG. 3 of the drawings, or
of a different type, such as that disclosed in PCT/AU2004/000637,
PCT/AU2005/001723 or PCT/AU2008/001697 the alignment of the
components of the system, eg a light source with the target and the
reflection of an emitted beam back to the receiver is important. As
mentioned above, there can be a significant distance between the
source and the target, thus aligning the light source accurately
with the target can be difficult. For this reason it is preferable
that an adjustable mounting arrangement is provided which allows
the direction of the light source (and/or target--if it is not
retro-reflective) to be varied, both at the time of installation,
and in the event that movement of the light source and/or the
target from its installation position occurs.
[0469] FIG. 17 depicts one embodiment of an alignment beam
arrangement which will assist in the alignment of the optical
components of a particle detector. The device depicted in FIG. 17
is of a type discussed above with respect to FIG. 2, but the smoke
detector can take various different forms. As shown, the smoke
detector 2200 includes the light source 2202 and a receiver 2204.
In addition, the smoke detector 2200 includes a visual alignment
device 2230 of the type adapted to generate an alignment beam 2242
which is axially aligned with the light source 2202 but which is
visually observable. The beam 2242 will project onto the target
2206 located some distance away from the smoke detector 2200.
[0470] The smoke detector 2200 is provided with a mounting means in
the form of a circular plate 2232 which in use will be mounted by
screws or the like to a support surface in order to fix the smoke
detector 2200 at a appropriate elevation to that support surface.
An articulated connection 2234 is provided between the mounting
plate 2232 and the smoke detector 2200. The articulated connection
can take various forms, which will allow the alignment of the
detector to be varied, but being lockable in the selected
orientation. A friction lock arrangement is possible, or some form
of screw tightening arrangement might be used.
[0471] As shown in FIG. 18, the articulated connection 2234
comprises a cup 2236 and ball 2238, the ball being able to rotate
within the cup. The ball is captively held by the cup so as to
allow the smoke detector 2200 to be tilted relative to the support
plate 2232, thereby allowing the incident light 2210 to be directed
precisely to the target 2206 some distance away. A grubscrew 2240
is provided for locking the ball relative to the cup. Other forms
of locking the ball in the cup are possible, including, for example
a friction fit.
[0472] As mentioned, the alignment beam 2242 is used to facilitate
the alignment of the incident light 2210 with the target. Thus, the
alignment beam 2242, which would typically comprise a laser beam,
is parallel to the incident light 2210. An operator would thus be
able to point the alignment beam 2242 at the target or just
adjacent to the target to thereby ensure that the incident light
2210 (which is typically not visible) is aimed centrally at the
target. Once the incident light 2210 is aimed at the centre of the
target, the grubscrew 2240 will be tightened, thereby locking the
ball 2238 within the cup 2236. This will ensure that the smoke
detector 2200 is optimally aligned and calibration of the system
can then take place in the manner described herein.
[0473] FIG. 19 of the drawings depicts a manner of securing the
smoke detector 2200 in a selected operable position. In this
embodiment, the grubscrew 2240 used for locking the ball 2238
within the cup 2236 is accessible along a passage 2244 extending
through to the front side 2246 of the detector housing 2200. The
passage 2244 is configured to receive the shaft 2248 of an
alignment tool 2250. The alignment tool 2250 has a driver 2252 on
one end thereof and a handle 2254 on the other end thereof. The
handle 2254 has a recess 2256 in the rear end thereof into which a
laser 2258 has been inserted. The shaft 2248 is a close sliding fit
with the passage 2244 such as when the shaft is located in the
passage 2244 the laser beam 2242 from the laser 2258 is axially
aligned with the light source 2202 and/or receiver 2204, as
discussed above.
[0474] In this embodiment the shaft 2248 and the passage 2244 each
have a complementary cylindrical shape. Of course the person
skilled in the art will appreciate that other arrangements are
possible, for example passage 2244 may have a square profile, the
side dimension of the square corresponding to the diameter of the
shaft 2248.
[0475] The installer, using the tool 2250 depicted in FIG. 19, will
thus insert the shaft 2248 into the passage 2244 and then
manipulate the housing 2200 whilst observing the visible alignment
beam 2242 at a remote target. When the housing is correctly
aligned, the handle 2254 will be rotated with driver head 2252
engaged with the grubscrew 2240 to thereby tighten the grubscrew
2240 and lock the cup and ball together. Once locked together in
this way, the technician installing the equipment will check that
the laser beam 2242 which is still correctly aligned with the
target, and if so, will know that the smoke detector is correctly
orientated. Clearly, at any time in the future, such as whenever
the equipment is to be maintained or serviced, the orientation of
the unit can be checked by simply inserting the shaft of the tool
2250 into the passage 2244 and checking, once again, whether the
laser beam 2242 is correctly aligned with the target on the remote
location.
[0476] In this embodiment, the driver 2252 is shown as a screw
driver head, but clearly if the grubscrew has some other form of
engagement formation, such as an Allen key socket, then the driver
2252 will be in the appropriately sized six sided Allen key
configuration.
[0477] Whilst FIG. 19 depicts a tool having a laser installed
therein for alignment purposes, it will, of course, be possible
simply to insert a laser 2258 into the passage 2244 to assist with
alignment of the housing relative to the remote target.
[0478] FIGS. 17 to 19 depict an arrangement in which the beam is
aligned parallel to the incident light beam but this is not the
only possible arrangement. For example, the housing may have a
plurality of laser receiving sockets therein angled to the incident
beam in a configuration which assists in the set up and orientation
of the smoke detector relative to a remote target or area of
interest. For example, where the smoke detector is of the form
discussed above with reference to FIG. 3, then it may be desirable
to have a laser beam which also indicates the full arc 2622 of the
light source illumination. Clearly it would be possible to include
a socket in the housing 2200 at an angle to the incident beam which
will correspond to the full arc of the light source
illumination.
[0479] FIG. 20 depicts diagrammatically a housing having three
sockets 2249, each of which is adapted to receive a tool 2250 shown
in FIG. 19 so as to enable the installation technician to correctly
align the housing for optimal performance. The lateral two sockets
2249 are preferably aligned relative to the arc of visible light
which the video camera is able to detect, and the central socket
will be used to align the centre of the video camera with the
target 2206 at the remote location.
[0480] FIG. 21 depicts a further embodiment of the invention. In
this embodiment the visual alignment device 2260 includes a shaft
2262 which in turn is mounted in a socket of the smoke detector
housing 2264 and will be aligned in fixed orientation to the
optical components mounted in the housing 2264. A video camera 2266
is mounted in a handle portion 2268 at the end of the shaft 2262.
The video camera will preferably be battery powered, and is adapted
to generate an image of a target at a location remote from the
housing 2264. The video camera is preferably provided with a
telescopic lens.
[0481] The image viewed by the video camera is preferably
transmitted wirelessly to a receiver unit 2270 which includes a
screen 2272 on which the image of the remote target is displayed.
The image may also include a sighting symbol or device 2274 which
may be in the form of cross-hairs, or some other form of alignment
assisting sighting device, such as a grid pattern or the like.
[0482] Clearly, when the housing is moved the field of view of the
video camera and hence image generated via the video camera will
move on the screen, and the technician doing the alignment of the
smoke detector will be able to correctly orientate the housing by
viewing the image on the screen. Since the video camera is aligned
in a fixed relative alignment to the optical components of the
smoke detector, once the image on the screen is correctly aligned
with the intended target, the technician will know that the optical
components are correctly aligned. The receiver unit is preferably a
hand held, battery powered computer device such as a PDA or the
like, showing real time images from the camera. The connection
between the camera and the receiver will preferably be wireless,
but could also be via cable.
[0483] The camera may be fitted with a wavelength dependent light
filter, at a wavelength that corresponds to a light source, such as
a LED, or other active or passive light source, mounted at the
target position. The target light source may flash, optionally at a
specific rate or pattern, so as to be readily discernable to the
human eye. The pattern of flash may also be identified by software
in the camera and/or the receiver.
[0484] The software in the receiver unit and or the camera may
include means for generating an enhanced view of the target on the
display, and may include surrounding images of the room or surface
on which the target is mounted. The receiver unit and camera
combination preferably includes means for generating audible sound
cues and/or voice instructions to the operator to assist in the
alignment process. These instructions may be in the nature of
instructions on how to move the housing so as to correctly align
with the target, and could include audible words such as `up`,
`down`, `left`, `right`, `on target`, and the like.
[0485] It will be appreciated that, with the video camera mounted
at the end of the shaft 2262, a small movement of the housing about
articulated connection 2274 will move the video camera at the end
of the shaft through a relatively wide arc. The shaft thus acts as
a lever arm, with the video camera mounted on the distal end of the
arm. This increases the sensitivity of the alignment process, so
that, provided the video camera and optical components are in the
correct relative alignment, when the video camera is correctly
aligned with the target the optical components will be precisely
aligned in the intended orientation.
[0486] FIG. 22 shows an alternative housing configuration for
optical components made in accordance with an embodiment of the
present invention.
[0487] In this example the component 2900 includes an
electro-optical component, such as a camera or light source(s) and
its associated electronic circuitry and optics 2904. The
electro-optical component 2902 is mounted in a fixed relationship
with respect to the housing 2906 and is connected via fixed wiring
2908 to electrical and data connections 2910.
[0488] The housing 2906 includes an aperture 2912 through which a
beam of light may enter or exit the housing. The aperture 2912 may
be open or can be closed by a lens or window. The component 2900
also includes an optical assembly 2914 mounted to the housing 2906.
The optical assembly, in this case, is a mirror mounted at an angle
with respect to the optical axis of the electro-optical system
2902, 2904. The mirror is used to redirect an optical signal either
to or from the electro-optical system 2902, 2904 and through the
aperture 2912.
[0489] The mirror 2914 is mounted to the housing 2906 via an
articulated mounting means 2916. The articulated mounting means in
this case comprises a rotatable shaft mounted in a rotation
friction bearing 2918 which is captured in a corresponding shaped
recess 2920 in the housing 2906. The articulated mounting 916
includes an engagement means 2922 which can be engaged from the
outside of the housing 2906 using an alignment tool. For example,
an alignment tool described in relation to the previous embodiments
can be used.
[0490] In use, a technician installing the optical component uses
the fixed mounting means to attach the housing in a fixed manner
with respect to a mounting surface and then adjusts the external
field of view (or illumination) of the electro-optical components
2902 by adjusting the orientation of the mirror 2914 using an
alignment tool. The method of operation of the system is
substantially the same as that described above except that the
articulated connection enables the orientation of the optical
assembly 2914 to be changed with respect to the electro-optical
component which is mounted in a fixed relationship with the
mounting surface, rather than enabling realignment of the entire
housing with respect to the mounting surface.
[0491] FIG. 23 illustrates a beam-detector assembly 2300 which may,
for example, be a light transmitter. The assembly 2300 is
constructed in two modules. Module 2302 is a main enclosure housing
a battery (not illustrated) and the electro-optical system 2306 for
the unit. The electro-optical system 2306 may be mounted on a
circuit board 2308. Module 2302 also includes a switch 2310 that,
in one arrangement, is responsive to magnetic fields. An example of
such a switch is a reed switch, which has of a pair of contacts on
ferrous metal reeds positioned in a hermetically sealed glass
envelope. The contacts are initially separated. In the presence of
a magnetic field the switch closes. Once the magnetic field is
removed, the stiffness of the reeds causes the contacts to
separate.
[0492] Other switching devices that are sensitive to magnetic
fields, such as Hall-effect devices may also be used.
[0493] Module 2304 is a mounting base, which includes an actuator
capable of acting on the switch 2310. The actuator may, for
example, be a magnet 2312.
[0494] The modules 2302 and 2304 are transported and stored
separately from one another or in a package where the actuator is
separated from the switch by sufficient distance to prevent
activation of the switch. Typically, at installation, the module
2304 is affixed to a wall 2320 or mounting surface and the module
2302 is then attached to module 2304. It will be appreciated that
there are many arrangements that enable module 2302 to be easily
and securely mounted to module 2304. For example, module 2304 may
have one or more tracks and, during assembly, the module 2302 may
be slid along the tracks as far as a stopper. A detent means may be
provided to hold the two modules in position. Such arrangements
allow the two modules to be assembled in a predetermined
orientation, thus positioning the switch 2310 relative to the
magnet 2312.
[0495] Only when the modules 2302 and 2304 are assembled is the
switch 2301 closed, permitting significant power consumption from
the battery to begin.
[0496] In another arrangement, module 2304 includes a plurality of
magnets 2312. The configuration of magnets 2312 may be used to
represent an item of information, such as identifying data for the
module 2304. The information may include a serial number or a loop
address associated with the location of the module 2304. By
providing a pattern of magnets on the base module 2304, the data
may effectively be retained permanently at the location where
module 2304 is attached to the wall 2320. Thus, even if the module
2302 is replaced, for example after a fault such as a depleted
battery, the identifying data is still present.
[0497] The module 2302 may include a plurality of switches 2310 or
sensors sensitive to the presence of the magnets 2312 in module
2304. For example, an array or predetermined pattern of reed
switches may be provided, capable of reading the identification
data coded in the pattern of magnets in module 2304.
[0498] In a further arrangement, the pattern of magnets 2312 in
module 2304 may be provided on a removable device, such as a card.
The card with the pattern of magnets may, for example, be inserted
into the module 2304 when the module is affixed to the wall
2320.
[0499] FIGS. 24 to 26 illustrate an alternative embodiment of the
invention. The transmitter unit 3000 includes a housing 3200,
forming an optical module. The transmitter further includes a
backing plate 3010, rear casing 3020 and forward casing 3030 which
together form a mounting portion 3180.
[0500] The backing plate 3010 includes screw holes through which it
may be mounted to a mounting surface (not shown) such as a wall.
The backing plate 3010 is attached to the rear casing 3020 with a
simple, releasable, snap fit.
[0501] The rear casing 3020 and forward casing 3030 together define
a partial spherical cavity in which the housing 3200 is received.
The housing 3200 includes a rear housing 3040 and a forward housing
3050.
[0502] Each of the rear and forward housing 3040, 3050 has a
predominantly hollow hemispherical shell like form.
[0503] The rear housing 3040 has a lip about its outer periphery.
The forward housing 3050 a complementary lip on the interior of its
outer periphery. The complementary lips are snap fitted together to
define the spherical housing 3200. Adjacent this snap fit a small
portion of the rear housing 3040 projects into the forward housing
3050 and defines an annular step thereabouts.
[0504] The outer surface of detector housing 3200 is predominantly
spherical and complementary to the spherical cavity defined by the
rear casing 3020 and the forward casing 3030. There is a close
sliding fit between the complementary spherical surfaces so that
the housing 3020 may be rotated to a wide range of orientations
relative to the mounting portion 3180 and loosely frictionally held
in alignment during installation.
[0505] A forward end of the forward casing 3030 is open to expose
the housing 3200. In this embodiment the opening in the forward
casing 3030 is shaped, and curved, to allow the housing 3200 to be
articulated to a wider range of angles about a vertical axis than
about a horizontal axis: typically such transmitters are wall
mounted close to the ceiling, as are the corresponding receivers,
it follows that generally less adjustment is required about a
horizontal axis, i.e. in the up and down direction.
[0506] A forward end of the forward housing 3050 is truncated to
define a circular opening in which a lens 3060 is carried. A
circular printed circuit board (PCB) 3070 is centrally mounted
within and spans the housing 3200. The PCB 3070 is parallel to the
lens 3060 and seats against the annular step defined by the rear
housing 3040 projecting into the forward housing 3050.
[0507] A light source in the form of LED 3080 is centrally mounted
on a forward surface of the PCB 3070 and in use projects a beam of
light e.g. in one or more wavelength bands, the obscuration of
which provides an indication of the presence of particles. The lens
3060 is arranged to collimate the beam projected by the LED 3080. A
battery 3090 is carried on a rear face of the PCB 3070.
[0508] The illustrated embodiment includes a locking mechanism 3190
including a spindle 3240, a cam 3100 and a brake shoe 3110
illustrated in FIG. 25. The spindle 3240 has at its axial mid point
an outwardly projecting collar 3140.
[0509] Each of the rear housing 3040 and the forward housing 3050
include a tubular recess for receiving a respective portion of the
spindle 3240. The collar 3140 is captured between the rear housing
3040 and the forward housing 3050 when the rear and forward
housings are snap fitted together. O-ring seals around the spindle
fore and aft of the collar 3040 limit the ingress of debris into
the housing 3200 via the tubular recesses.
[0510] A hexagonal socket 3160 is formed in a forward end face of
the spindle 3240. A cylindrical tubular passageway 3244 passes
through the forward housing 3050 and provides access to the socket
3160. The socket 3160 during installation of the transmitter unit
receives an Allen key like fitting from the front of the
transmitter unit 3000 via the passage 3244 so that an installer may
rotate the spindle 3240 about its axis. As will be described, said
rotation locks the housing 3200 in a selected orientation relative
to the mounting portion 3180.
[0511] The rear housing 3040 has a rearward aperture in which is
carried a brake shoe 3110. The brake shoe 3110 has an outer surface
3130 which is part spherical and aligned with the spherical outer
surface of the rear housing 3040 when in a retracted `articulating
position`. The brake shoe 3110 carries a stud 3120 on each of its
sides. The studs 3120 project a short sideways distance, i.e. in
directions perpendicular to the up and down and fore and aft
directions. The studs 3120 are received within complementary
recesses (not shown) in the rear housing 3040 and thereby define a
pivot about which the brake shoe 3110 may rotate through a range of
motion. The range of motion is limited by contact between the
braking surface 3130 and the internal spherical surface defined by
rear and/or forward casings 3020, 3030, and by contact with a cam
3100 described below.
[0512] As illustrated in FIG. 25 the brake shoe 3110 includes a
central longitudinal channel separating two wing portions which
each carry a respective stud 3120. The brake shoe 3110 has a degree
of compliance so that the brake shoe 3110 and the rear casing 3040
may be assembled by compressing the wing portions, to reduce the
overall dimension across the studs 3120, and fitting the brake shoe
3110 to the rear casing 3040 so that the studs 3120 are received
into the complementary recesses (not shown) formed in the rear
casing 3040. Once released the wing portions return to their
uncompressed shape so that the studs 3120 snap into the
complementary recesses.
[0513] The cam 3100 is carried by the spindle 3240. Of course
another option would be for the cam to be integrally formed with
the spindle as illustrated in FIG. 28. The cam 3100 includes a
single lobe and is arranged to act downwardly on the brake shoe
3110 at a location forwardly spaced from the studs 3120 (and a
pivot axis defined thereby).
[0514] During installation of the receiver 3000, after aligning the
housing 3200, an installer accesses socket 3160 of spindle 3240 via
the passage 3244 with an Allen key like tool. Using the Allen key
like tool to rotate the spindle 3240 rotates the cam 3100, which in
turn drives the forward portions of the brake shoe 3110 downwardly
so that the braking surface 3130 frictionally engages the internal
spherical surface defined by rear and forward casings 3020 and
3030. The alignment of the housing 3200 relative to the mounting
portion 3180 is thereby locked.
[0515] In this embodiment the lens 3060 and LED 3080 are configured
to project light in a direction perpendicular to the plane of the
lens 3060. The passageway 3244 is also perpendicular to the plane
of the lens 3060. During installation an alignment tool, similar to
those described above, may be used, wherein the alignment tool has
a cylindrical shaft sized for a close sliding fit with the passage
3244 and includes a laser pointer arranged to project a beam
coaxial with the shaft. In this embodiment the shaft of the
alignment tool terminates in an Allen key fitting complementary to
the socket 3160. During installation the tool is inserted into the
passage 3244 and engaged with the socket 3160. When engaged, the
alignment tool can be used as a lever and may be manipulated until
its projected beam is focused on a target, such as a receiver. The
passage 3244 thereby provides a convenient means for providing a
visual indication of the alignment of the housing 3200. The
alignment tool may then be simply rotated about its axis to lock
the housing 3200 in the correct alignment.
[0516] As previously described, it is desirable that the power
supply, in this case the battery 3090, is only connected (to
activate the transmitter) upon installation. The collar 3140 of
spindle 3240 carries at a point on its circumference a magnet 3150.
The relative position of the magnet 3150 and the lobe of the cam
3100 is selected so that when the brake shoe 3110 is in an
advanced, `braking`, position the magnet 3150 interacts with a reed
switch (not shown) mounted on a rear face of the PCB 3070 to close
the switch and thereby connect the power supply and activate the
receiver 3000. The location of the magnet about the collar 3140
relative to the lobe of the cam 3100 is selected so that when the
brake shoe 3110 is in the retracted, `articulation`, position the
magnet 3150 does not act on the reed switch, so that the reed
switch remains open, and the receiver remains inactive.
[0517] The transmitter unit 3000 is simple to install. The receiver
3000 can be supplied as a preassembled unit--with the locking
mechanism in the retracted, articulation, position so that the
battery is not connected and does not run down. The backing plate,
which is attached to the rear casing 3020 with a simple snap fit is
levered off (i.e. unsnapped) and screwed or otherwise fastened to a
wall or other mounting surface. The rear casing 3020, and the
remainder of the receiver 3000 attached thereto, is then simply
snapped onto the backing plate. The housing is then aligned using
the aforedescribed alignment tool and then easily and conveniently
locked in said alignment and activated with a single motion of the
same tool.
[0518] FIGS. 27 and 28 illustrate a further alternative embodiment
of the invention similar to the embodiment described in FIGS. 24 to
26. FIG. 28 is analogous to FIG. 25 however it illustrates a
receiver 3000' useable in an embodiment of the present invention.
Receiver 3000' includes a passage 3244' through which a spindle
3240' may be accessed as in the previous embodiment. This
embodiment differs from the embodiment of FIG. 24 in the details of
the locking mechanism. The spindle 3240' includes an integrally
formed cam 3100' arranged to act on a pivotally mounted lever arm
3210.
[0519] The lever arm 3210 has a length in the sideways direction,
i.e. perpendicular to the up and down and fore and aft directions.
A stud at 3120' projects forwardly from one end of the lever arm
3210. The stud 3120' is received within a complementary recess (not
shown) defined within the transmitter housing 3200' at which the
lever arm 3210 is pivotally supported within the transmitter
housing 3200'.
[0520] Short studs 3230 project in the fore and aft directions from
the other end of the lever arm 3210. The studs 3230 are coaxially
aligned. A brake shoe 3110' including an upwardly projecting clevis
arrangement embraces the other end of the lever arm and engages
with the studs 3230 to pivotally connect the lever arm 3210 and
brake shoe 3110'. The brake shoe 3110' projects downwardly from the
lever arm 3210, and has a square cross section and determinates in
a part spherical braking surface 3130'.
[0521] The brake shoe 3110' is seated within and guided by a
tubular through hole (not shown), having a complementary square
profile, within the transmitter housing 3200'.
[0522] During installation of the transmitter 3000' the spindle
3240' is rotated, as in the previous embodiment. As the spindle
3240' is rotated the cam 3100' acts to drive the lever arm 3210
downwardly about its pivot axis (defined by the stud 3120'). The
braking shoe 3110' is in turn pushed downwardly to frictionally
engage an internal surface of the fixed mounting portion 3180'.
[0523] The lever arm 3210 includes an integrally formed finger 3220
projecting downwardly, from the end of the lever arm 3210, at an
acute angle from a main body of the arm. The finger 3220 defines a
curved path an outer surface of which is complementary to an
interior of the transmitter housing 3200'. The finger 3220 is
dimensioned to press against said interior and thereby bias the
lever arm 3210 to rotate upwardly about its pivot axis (defined by
the stud 3120'). The brake shoe 3110' is thereby biased against the
cam towards a retracted, non-braking, position.
[0524] As noted previously the soiling of optical surfaces over
time can cause problems in beam detectors. To address this problem
the inventors have determined that the system can be adapted to
compensate for soiling of the optical system over time. FIG. 29
illustrates how the true received light level i.e. the level of
light arriving at the system's receiver or light sensor decreases
over time. FIG. 29 shows a plot between times t1 and t2 of the true
light level arriving at a sensor of a beam detector receiver over
time. As can be seen from the plots the received light level at
wavelengths .lamda..sub.1 and .lamda..sub.2 decrease gradually over
time due to the build up of contamination on the surfaces of the
optical system of the receiver. To compensate for the loss of
sensitivity, in one embodiment of the present invention, the system
gain is correspondingly increased very slowly over time (as
indicated in FIG. 30) such that the detected intensity
.lamda..sub.1 and .lamda..sub.2 remains substantially stable over
time.
[0525] FIG. 31 is similar to that of FIG. 30 except, as can be seen
the degradation in performance in wavelength bands .lamda..sub.1
and .lamda..sub.2 are different. In this embodiment, the signal at
.lamda..sub.2 is more greatly influenced by the contamination of
the optics than that at .lamda..sub.1. In such a scenario, a system
which uses a differential, or relative value between the received
signals in two wavelength bands as likely to go into a false alarm
state as the separation between the received signal at wavelength
.lamda..sub.1 and .lamda..sub.2 increases. To address this problem,
the gain is adjusted differently for each wavelength, and as can be
seen when the gains are adjusted, as in FIG. 30 the long term
average output of the system remains substantially constant.
[0526] In the examples of FIGS. 31 and 32 a smoke event 3500 occurs
approximately midway between times t1 and t2. In this case, because
.lamda..sub.1 effectively operates as a reference wavelength it
undergoes a very minor drop in intensity whereas the received
signal at .lamda..sub.2 undergoes a very marked drop due to
.lamda..sub.2's tendency to be more strongly absorbed by small
particles. As can be seen, because the smoke event has such a short
duration in comparison to the compensation being applied to the
gains the long term compensation for system contamination is not
affected by the occurrence of the smoke event 3500 and the smoke
event 3500 is also reliably detected by the system.
[0527] Referring to FIGS. 33 to 35, a light source 3300 according
to an embodiment of the present invention is depicted. The light
source 3300 includes a housing 3302 with a transmission zone 3304
through which light is transmitted from the light source 3300 to a
receiver 3306.
[0528] The transmission zone 3304 is in this instance located on
the exterior of the housing 3302 and provides the point at which
light from within the housing 3302 is transmitted from the light
source 3300 towards the receiver 3306. As such, the transmission
zone 3304 is accessible from outside the light source 3300 and may
be affected by dust/dirt build up, insect/bug activity etc. The
transmission zone 3304 may, without limitation, be any optical
surface (or part thereof), and while for illustration purposes has
been depicted as protruding from the housing 3302 it may, of
course, be flush with or recessed within the walls of the housing
3302. The transmission zone 3304 may be integral with the housing
3302 or may be a component part thereof.
[0529] In the present embodiment the housing 3302 houses a first
light emitter 3308, a second light emitter 3310 and a third light
emitter 3312. Each light emitter 3308 to 3312 is an LED and emits a
beam of light (3314, 3316 and 3318 respectively) which is
transmitted through the transmission zone 3304 to the receiver
3306. The first light emitter 3308 and third light emitter 3312
emit electromagnetic radiation in a first spectral band, e.g. UV
light (i.e. light in the ultraviolet portion of the EM spectrum) of
substantially equal wavelength, and as such shall be referred to as
UV emitters. The second light emitter 3310 emits EM radiation in a
second spectral band, e.g. IR light (i.e. in the infrared portion
of the EM spectrum) and as such shall be referred to as a IR
emitter. Correspondingly, light beams 3314 and 3318 will be
referred to UV light beams and light beam 3316 will be referred to
as a IR light beam.
[0530] The light source 3300 also includes a controller 3320
adapted to control operation of the first, second and third light
emitters 3308 to 3312. The controller may be housed within the
housing 3302 as shown, or may be remote from the housing and
control operation of the light emitters 3308 to 3312 remotely.
[0531] As will be appreciated, the specific manner in which the
light emitters 3308 to 3312 are operated by the controller 3320
depends on the programming of the system. In this embodiment the
controller 3320 alternates operation of the light emitters 3308 to
3312 in a repeating alternating sequence. The processing of these
beams as received by the receiver 3306 is discussed in further
detail below.
[0532] The controller may also be adapted to operate one or more of
the light emitters 3308 to 3312 to send a control signal to the
receiver 3306. Such a control signal may indicate status
information regarding the light source 3300, for example, convey
that the light source 3300 is operational, that the light source
3300 is malfunctioning, and/or that the light source 3300 battery
is running out. The control signal may be determined by the timing
and/or intensity of the light beams 3314, 3316 and/or 3318 as
emitted by respective light emitter 3308 to 3312.
[0533] As can be seen, the UV light emitters 3308 and 3312 are
separated from each other which, in turn, leads to a separation of
the point at which the UV light beams 3314 and 3318 leave the
transmission zone 3304. The separation between the UV light
emitters (and UV light beams 3314 and 3318) is of sufficient
distance such that if the transmission zone 3304 is obstructed by a
foreign body 3322 only one of the UV light beams 3314 or 3318 may
be obstructed. A separation of approximately 50 mm between the
first and third light beams 3314 and 3318 has been found suitable
for this purpose. Thus, this arrangement effectively provides a
redundant light emitter in the UV band.
[0534] The term "foreign body" is used here to refer to objects or
nuisance particles larger than dust or smoke particles or other
particles of interest that may be present in the air. As one
example, a foreign body obstructing the transmission zone 3304 may
be an insect or bug crawling over the transmission zone 3304.
[0535] FIG. 34 shows an example of a single UV light beam 3318
being obstructed, with the remaining IR light beam 3314
unobstructed. In this instance the receiver 3306 recognises a fault
condition because it only received every second expected UV pulse
rather than an alarm condition.
[0536] Should this condition (i.e. the condition where only one of
the UV light beams 3314 or 3318 is being received at the receiver
3306 or is received at a significantly lower level than the other
due to partial obstruction) persist for a significant time, e.g. 1
minute, the receiver 3306 may be programmed to interpret this as an
error/malfunction with the light source 3300 and trigger an
appropriate alarm/error message.
[0537] In contrast to the obstruction shown in FIG. 34, FIG. 35
depicts the situation where smoke particles 3324 in the air
obstruct all three beams 3314 to 3318. In this instance the smoke
3324 attenuates each of the light beams 3314 and 3318 to
substantially the same extent, and the usual alarm logic can be
applied to determine whether an alarm or fault condition
exists.
[0538] FIG. 36 provides an alternative to the above embodiment. The
light source 3600, similarly to the previous embodiment includes a
housing 3602 and a transmission zone (or window) 3604 through which
beams 3614, 3616 and 3618 are emitted to a receiver 3606. The
operation of the light source 3600 is controlled by a controller
3620. UV light beams 3614 and 3618 are emitted from a single UV
light emitter 3626. In this case the light source 3600 includes a
beam splitter 3628 which splits the beam from light source 3626
such that the first and third light beams 3614 and 3618 exit the
transmission zone 3604 at a sufficient distance from each other as
described above.
[0539] Turning to FIGS. 37 to 40, a further alternative embodiment
of a light source 3700 for use in a particle detection system is
provided. Light source 3700 includes a housing 3702 with a
transmission zone 3704 through which light is transmitted from the
light source 3700 to a receiver 3706. The transmission zone 3704 is
as described above in relation to transmission zone 3604, however
as can be seen is much smaller.
[0540] Housing 3702 houses first and second LED light emitters 3708
and 3710. Light emitter 3708 is a UV light emitter and emits a UV
light beam 3712, while light emitter 3710 is an IR light emitter
and emits IR light beam 3714. The light source 3700 also includes a
controller 3716 adapted to control operation of the first and
second light emitters 3708 and 3710. The controller may be housed
within the housing 3702 as shown, or may be remote from the housing
and control operation of the light emitters 3708 and 3710
remotely.
[0541] As can be seen, the light source 3700 is configured (as
described below) such that the light beams 3712 and 3714 leave the
light source from the transmission zone 3704 along substantially
the same path. Most preferably they are co-linear. This arrangement
provides the feature that if the transmission zone 3704 is
obstructed by a foreign body 3718 as shown in FIG. 38 (again, for
example, an insect crawling across the transmission zone) the UV
and IR light beams 3712 and 3714 are obstructed to a substantially
equivalent degree.
[0542] When a foreign body 3718 obstructs the transmission zone
3704 it causes substantially equal obstruction to both the first
and second beams 3712 and 3714, and the controller associated with
the receiver will apply alarm and or fault logic to determine the
cause of the decreased received light level. The fault and alarm
logic can be configured to interpret an equivalent and simultaneous
drop in received intensity in the following manner. In some cases
with a small drop in intensity the system may interpret this as a
fault or obstruction. If the condition persists it can be
compensated for in software or a fault condition raised. With a
large drop in intensity an alarm may be raised, even though the
primary alarm criteria are based on differential attenuation of the
two wavelength bands as described in our co-pending patent
application.
[0543] FIGS. 37 and 38 provide one embodiment of a light source
3700 configured to provide beams 3712 and 3714 that leave the light
source 3726 from the transmission zone 3704 along substantially
co-linear paths. In this embodiment light beams 3712 and 3714 do
not originate from light sources 3708 and 3710 that are physically
proximate, but are brought into proximity with each other prior to
reaching the transmission zone with light directing optics 3722.
Light directing optics 3722 may be any optics suitable for
directing light, such as mirrors, lenses (e.g. convex, concave,
Fresnel lenses) and/or prisms, or a combination thereof, and may
also serve to collimate light beams 3712 and 3714.
[0544] FIG. 39 provides an alternative embodiment of a light
emitter 3724 configured such that the light beams 3712 and 3714
leave the light source from the transmission zone 3726 close
together. In this embodiment the first and second light emitters
3728 and 3730 are semiconductor dies housed within a single optical
package 3732 (the transmission zone 3726 being the point at which
the emitted light beams 3712 and 3714 exit the package 3732). In
this embodiment the proximity of light beams 3712 and 3714 is
achieved by the physical proximity of the semiconductor dies 3728
and 3730 within the package 3732 and the leasing effect of the
package 3732.
[0545] This may be achieved by using an LED with multiple
semiconductor dies in a common LED package. Examples are depicted
in FIGS. 47 to 49. As with typical LED's, the housing is made of a
clear material and shaped so as to have a lens effect on the
emitted light beams that broadly constrains the beams to a forward
direction.
[0546] In a further embodiment, and as shown in FIGS. 41 and 42,
the light source 3700 is also provided with beam shaping optics
4102 for adjusting the shape of light beams emitted from light
emitters 3708 and 3710. Whilst depicted as a single element in FIG.
41, the beam shaping optics 4102 may in practice (and as shown in
FIG. 42) include a number of beam adjusting elements serving
variously to adjust the beam width and/or beam shape of light
transmitted from the light source 3700 to the receiver 3706.
[0547] Light beams 3712 and 3714 (from light emitters 3708 and
3710) pass through the beam shaping optics 4202 which function to
provide an adjusted beam 4104 with desired characteristics as
discussed below.
[0548] As will be appreciated a beam will have a spatial intensity
profile, or beam profile, in a direction transverse to its axis.
Using the beam profile a beam width of a light beam can be defined
between two points of equivalent intensity e.g. between the 3 db
points either side of a maxima etc. One common measurement of beam
width is the "full width at half maximum" (FWHM) of the beam. For
example, the adjusted beam 4204 in FIG. 42 is shown as having a
wide section 4214 in which the intensity of the beam 4204 is above
the predetermined threshold (depicted in black) fringed by lighter
beam sections 4216 where the intensity of the beam is below the
predetermined threshold.
[0549] The beam shaping optics 4102 can be chosen to achieve a
desired beam profile, and a collimating element 4208 serving to
collimate light beams 3712 and 3714 into a tighter beam shape. The
collimating element 4208 may, for example, be a lens such as a
Fresnel lens or a convex lens, or may be a reflector.
[0550] The beam adjusting optics can also include a diffusing
element 4210, selected to "flatten" the beam profile and increase
the beam width of the light beams 3712 and 3714. The diffusing
element can be for example a ground/etched/smoked glass diffuser.
The diffusing element 4210 may, alternatively, be a coating applied
to either the transmission zone 3704 or another beam adjusting
element.
[0551] FIG. 40 illustrates an exemplary optical element 4000 that
shapes and flattens the beam profile. The optical element 4000
includes a Fresnel lens 4080 placed back to back with a
multi-element lens 4081. The Fresnel lens collimates the beam and
the multi-element lens 4081 effectively diffuses the beam. In place
of the multi-element lens 4081 another diffuser eg. ground, smoked
or etched glass or surface could be used.
[0552] Providing a diffuser on the transmitter is advantageous as
the receiver will "see" an extended spot corresponding to the light
source, rather than a point, which would be observed without the
diffuser. Consequently, any foreign body (such as an insect)
landing on the transmission zone 3702 will cover a smaller
proportion of the transmission zone and therefore have a
proportionally smaller effect on the total light received at the
receiver 3706. Moreover, in a multiple beam system when all light
emitters (3708 and 3710, i.e. light at both the UV and IR
wavelength) are diffused through a common element any foreign body
(such as an insect) landing on the transmission zone 3702 will
effect each wavelength of the light (i.e. UV and IR) by
substantially the same amount.
[0553] Further by providing a greater beam width to the adjusted
beam 4204 alignment of the receiver 3706 with the light source 3700
is simplified. FIG. 43 provides a depiction of a receiver 4350
receiving a beam 4352 from a light source 4354. By having a wide
beam width the rate of change of intensity across the beam width
(near its centre) is reduced. This means that as alignment of the
beam and receiver drift over time, the rate of change in received
intensity near the centre of the beam, for small relative
movements, is reduced compared to a beam with a narrow beam
width.
[0554] In this case the beam width 4356 of the beam 4352
corresponds to about three sensor elements on the sensor 4350. If
the system is configured to average (or aggregate) output these
three pixels are used to determine the received beam's strength, a
small variation in alignment between the transmitter and received
will require either the system to accurately track the beam
movement on the sensor's surface or alternatively cause a large
variation in measured signal strength from the three pixels. This
problem's minimised using a wider beam width as shown in FIG. 44.
In this system the beam 4462 emitted by the light surface 4454 has
a width 4456 equal to about the size of 6 sensor elements on sensor
4450. As will be appreciated such a system is more tolerant to
alignment drift before the central 3 pixels lie outside the central
high intensity beam region.
[0555] The specific properties of the diffuser used and the beam
width provided will depend on the receiver and light emitters.
Using LED's, however a beam width of approximately 10 degrees has
been found to be a suitable compromise between the preservation of
intensity of the adjusted beam and width, so as to accommodate for
easy alignment of the receiver with the light source and drift of
the receiver and/or light source.
[0556] Referring to FIG. 42, the profile adjusting element 4212 is
selected such that the beam profile of the adjusted beam 4204
extends further in the horizontal direction than the vertical. This
serves to maximise the intensity of the adjusted beam 4204 at the
receiver whilst also accommodating for the fact that building
movement typically introduces more variation in the horizontal
plane than the vertical plane.
[0557] The light source can include a wavelength dependent profile
adjusting element 4212 for providing a different intensity profile
to beams in different wavelength bands. The beam adjustment element
may again be a lens, reflector, coating or similar selected to
provide the desired beam profile at each wavelength is
achieved.
[0558] The profile adjusting element 4212 has the effect of
producing an adjusted beam 4204 having a beam profile in which the
beam width of the UV light (originating from the UV emitter 3708)
is wider than the beam width of IR light (originating from the IR
emitter 3710). This is depicted in FIGS. 45 and 46 where the light
source 4500 transmits a beam 4502 in which the beam width of the UV
light 4504 is wider than the beam width of the IR light 4506. This
has the advantage that in the event that the light source 4500 or
receiver 4508 moves (e.g. due to building movement) and the
alignment therebetween is disrupted, the IR light 4506 (having a
narrower beam width) will move out of alignment with the receiver
4508 (i.e. reducing the amount of IR light received at the
receiver) before the UV light 4504 does. This produces a decrease
in IR light intensity at the receiver, followed by a decrease in UV
intensity as alignment become progressively worse. This is the
opposite to the effect seen when smoke enters the beam, when UV
drops before IR. Hence the misalignment can be distinguished from a
smoke event by the fault/alarm logic of the controller.
[0559] As an alternative to using a profile adjusting element, a
light source may be used with a plurality of UV light emitters
surrounding one or more IR light emitters. In this case as the
alignment of the light source and receiver is disrupted the
receiver will cease to receive IR light before it ceases to receive
the UV light beam, thereby allowing the receiver to interpret this
as a fault rather than an alarm event.
[0560] In some embodiments an exotic intensity profile can be
formed, e.g. an intensity profile having a sinc function or
similar. In this case if a sensor element or group of sensor
elements of the receiver's sensor detects a variation in received
beam intensity that matches the spatial intensity profile of the
transmitted beam, it can be determined by the controller that the
beam is sweeping across the sensor element or group of sensor
elements. This can be used by fault logic to detect and signal that
the system is drifting out of alignment and either re-alignment is
needed or soon will be needed.
[0561] FIG. 47 illustrates a light emitter 4740 which may be used
in a transmitter of a beam detector according to an embodiment of
the present invention. The light emitter 4740 includes a body 4742
in which is housed one or more light emitting elements (not shown).
The emitter 4740 includes a lens or window portion 4744 through
which the beams of light generated by the light emitting elements
are emitted. It also includes a plurality of leads 4746 for making
electrical connection to the device. FIG. 47 illustrates a plan
view of the same light emitter 4740. The light emitter 4740
includes a plurality of light emitting elements 4748, 4750. In this
case the light emitter is a LED and the light emitting elements are
two LED dies in the form of a UV LED die 4748 and an IR LED die
4750 which constitute the light emitting elements. The package 4740
also includes a photodiode 4752 within the body 4742. Each of the
light emitting elements 4748, 4750 are adapted to emit light
through the lens 4744. The photodiode 4752 receives some proportion
of the light emitted by the light emitting elements 4748, 4750 and
generates an electrical signal which is fed to a feedback circuit.
The photodiode output signal is used by the feedback circuit to
adjust the output of the light emitting elements to maintain
correct operation of the light emitter 4740.
[0562] FIG. 49 illustrates a second embodiment of a light source.
In this example, the light emitter 4955 includes a plurality of
light emitting elements arranged in a checkered pattern. In this
case, the light emitter 4955 includes four UV LED dies 4958
arranged around a central IR LED die 4960. As described above, this
arrangement may have particular advantages for preventing false
alarms caused by a misalignment of the light source with its
respective receiver. The package 4955 also includes a photo diode
4952.
[0563] FIG. 50 illustrates a schematic block diagram of circuit for
a transmitter which may be used in an embodiment of the present
invention. The circuit 5000 includes two light emitters 5002, 5004
which e.g. correspond to the infrared and UV LED dies as described
above. It also includes a photodiode 5006. As will be apparent from
the above description the LEDs and photodiode 5002, 5004, 5006 may
be packaged closely adjacent to each other within a single LED
package. However, they may also be separately packaged in
individual components. The light emitters 5002, 5004 are
electrically connected to a current source 5008 and the photodiode
5006 is electrically connected to a feedback circuit 5010. The
feedback circuit 5010 is in communication with the current source
5008. In use, the output from the photodiode 5006 which represents
the output of LEDs 5002, 5004, is passed to the feedback circuit
5010 which in turn controls the output of the current source 5008
to the light emitters 5002, 5004. As the received light signal at
the photodiode 5006 decreases, for example due to decreased light
output by the LEDs over time or through decreased light emission of
the light emitters 5002, 5004 due to an increase in temperature,
the feedback circuit 5010 will apply an output to the current
source 5008 which causes an increase in the drive current to the
light sources 5002, 5004. In this way, the light output of the
light emitters 5002, 5004 can be maintained at an approximately
constant level. Because the light emitters may have different
characteristics and predetermined illumination characteristics
required for correct system operation, the output of the two light
emitters 5002, 5004 can be individually controlled and adjusted.
This can be achieved by alternatively pulsing their illumination
and individually determining their light output using the
photodiode 5006. Alternatively, multiple photodiodes could be used
in a manner in which their response is wavelength selective, and
tuned to a corresponding light emitter. For example this may be
achieved by providing different bandpass filters over each of the
photodiodes. In this case, the light emitters 5002, 5004 can be
simultaneously illuminated and their outputs individually
stabilised using a feedback circuit as described herein. FIG. 51
illustrates the feedback procedure of the circuit of FIG. 50 in
stabilising the light output of one light emitter which is
continuously illuminated. The plot of FIG. 51 includes a first
portion 5102 which represents the output of the photodiode over
time and represents a decrease in light output from the light
source over time. This output is fed into the feedback circuit
which controls the drive current output by the current source 5008.
The decrease in the photodiode output causes an increase in the LED
output current as shown by plot 5104.
[0564] FIG. 52 illustrates a second circuit in a schematic block
diagram form. In this example, rather than controlling the output
current of the current source, the duration of output pulses of the
light emitters is controlled by the feedback circuit. Accordingly,
FIG. 51 includes two light sources 5202, 5204 each of which is
connected to a current source 5208. The circuit also includes a
photodiode 5206 which is connected to a feedback circuit 5210. This
circuit 5200 additionally includes a drive pulse modulation circuit
5212 which controls the timing and duration of the pulses of
current applied to the light emitters 5202, 5204 by the current
source 5208. In this example, when a decrease in the received light
level received by the photodiode 5206 is sensed the feedback
circuit 5210 applies a signal to the modulation circuit 5212. In
response, the modulation circuit 5212 increases the pulse length
produced by the current source 5208 that is applied to the
LEDs.
[0565] FIG. 53 illustrates the method of operation of the circuit
of FIG. 52. The top plot illustrates the output of the photodiode
5302, which as can be seen, generally decreases over time. The
lower plot 5304 illustrates the drive current applied to the light
emitters. In this case, the output current is applied in square
wave pulses e.g. 5306. As the output of the photodiode decreases
the duration of the pulses increases over time. By adjusting the
pulse duration in this manner and maintaining the current at a
constant level the effective light intensity transmitted by the
light emitters, when integrated over the pulse length remains
substantially constant. Advantageously it also results in more
accurate reception of the pulses at the receiver since rather than
the receiver simply taking a single sample of the light intensity
within each pulse the receiver can be operated as an integrator and
collects more of the transmitted signal.
[0566] The plots of FIGS. 51 and 53 illustrate the photodiode
response and drive circuit current for a single light emitting
element of the transmitter. A similar plot can be created for the
other (or others) light emitting elements.
[0567] In another embodiment of the present invention open loop
control of the LED intensity may be provided. For example, this may
be achieved at low cost by providing a current drive circuit that
is temperature stabilised or temperature compensated for the output
characteristics of the LED.
[0568] In a further embodiment of the present invention the output
of the light emitting elements may only be weakly controlled, for
example by being driven by a fixed pulse length with a very simple
current control circuit. In this case, the averaged output
intensity which is measured by the photodiode can be communicated
to the receiver. The receiver can then be configured to compensate
for the changing LED output in software. In a preferred form the
averaged LED output can be communicated to the receiver using an
optical communications channel or other wireless communications
channel. In a case where an optical communications channel is used,
this can be implemented by modulating the output of the light
emitters themselves by inserting or omitting pulses in the sequence
of illumination pulses of one or the other, or both of the light
emitters. This embodiment has the advantage of requiring only a
relatively low cost transmitter without complex feedback circuitry.
It also takes advantage of the fact that temperature and age
related drift of the light emitter outputs is likely to be
relatively slow so the bandwidth of the communications only needs
to be low.
[0569] A further problem that can arise in the methods described
above which use one or more photodiodes to measure and control the
output intensity of the light emitters is that ambient light may
interfere with this measurement. For example, sunlight may be
received by the photodiode and erroneously increase the detected
output light level of the light emitting element as detected by the
photodiode.
[0570] To overcome this problem, in one embodiment, the effective
ambient light can be greatly reduced by using a band pass filter in
conjunction with the photodiode. For example, a photodiode which
only passes light in a wavelength band emitted by its corresponding
light emitter, but which attenuates all other wavelengths e.g.
those commonly occurring in sunlight can be effectively used.
Similarly, if artificial lighting such as fluorescent lighting is
used, the band pass filter can be adapted to exclude substantially
all of the artificial light whilst still transmitting light in a
wavelength band transmitted by the corresponding light emitter.
[0571] In an alternative embodiment, light absorbing baffles may be
positioned around the photodiode e.g. in the LED package such that
only light from the light emitting elements can reach the
photodiode. The photodiode can be shielded from external light by
placing a baffle between the photodiode and the lens of the LED
package.
[0572] A further mechanism for correcting for background light
levels is to take measurements from the photodiode when the light
emitters are in `on` and `off` conditions. In this case
measurements taken during the `off` periods, between pulses of the
light emitters, represent the background light. This background
light level can be subtracted from the next (or previous) light
level measured during an `on` period i.e. a time period in which a
light emitter element is illuminated. The background light level
can be averaged over several `off` frames and a sliding average of
the background level subtracted from the `on` period data if
smoothing of the background light levels is required. For example,
this may be needed when the ambient light level varies greatly with
a frequency equal to or substantially equal to the pulse frequency
of the light emitters.
[0573] FIG. 54 illustrates a light source made in accordance with
an embodiment of the present invention. The light source 5400
includes a light emitter 5402 electrically connected to a control
circuit 5404 which is powered by a power source 5406. The light
emitter 5402 projects a beam (or beams) of light through an optical
system 5408 towards a receiver. In some embodiments, the optical
system 5408 may simply be a transparent window through which the
beam of light is projected in use, but also may be a more
complicated optical arrangement e.g. including one or more lenses,
mirrors or filters etc. that are adapted to cause the beam of light
emitted by the light source 5402 to take on particular beam
characteristics. As described above the external surface of the
optical component 5408 is prone to temporary occlusion by insects
or the like on its outer surface.
[0574] In order to detect these foreign bodies, the light source
5400 is provided with a photodiode 5410 or other light sensitive
element which is connected to the control circuitry 5404. In use
the photo diode 5410 is arranged such that it will receive
scattered light from foreign bodies occluding at least part of the
outer surface of the optical arrangement 5408. The photo diode 5410
is connected back to the control circuit 5404 which is adapted to
determine based on the integrity of the received scattered light by
photo diode 5410 whether a fault condition exists. For example the
control circuit 5404 can include a micro controller 5412 which is
programmed with, inter alia, fault logic which compares the
received feedback signal from the photo diode 5410 to a
predetermined threshold and if the received intensity is above the
predetermined threshold, or some other intensity and/or time based
criteria are met by the feedback signal, the fault logic can be
adapted to trigger a fault response in the light source 5400. For
example, the microcontroller may cause an illumination pattern of
the light emitter 5402 to change in response to the fault condition
to signal to a receiver of the particle detection system that a
fault condition exists. By encoding a particular signal in the
light emission patent the type of fault could be signalled back to
the receiver. The fault condition could be communicated by
modulating the amplitude, duration and/or the timing of the
transmitted light pulses in a predetermined fashion. This has the
advantage that no wiring or other wireless communication systems
are required between the transmitter and receiver of the particle
detection system.
[0575] FIGS. 55 and 56 illustrate alternative embodiments of this
aspect of the present invention, and common parts have been
numbered with common reference numerals.
[0576] Turning first to FIG. 55 which shows second embodiment of a
light source 5500 made in accordance with an embodiment of the
present invention. In this embodiment, the light source 5500 has
been provided with an additional light emitting device 5502. This
light emitting device is placed such that it illuminates the lens
from a shallow angle of incidence. This increases the chance that
particles or foreign bodies which fall on the external surface of
the optical component 5408 will produce a sufficient reflection to
be detected by the photo diode 5410. In this embodiment, the photo
diode can be shielded by a wall or baffle 5504 to prevent direct
illumination of it by the light source 5502.
[0577] FIG. 56 illustrates a light source 5600. This embodiment
differs from the light sources illustrated in FIGS. 54 and 55 by
the inclusion of an externally mounted light emitter 5602. This
light emitter 5602 is positioned such that it illuminates the
outside surface of the optical component 5408 directly. This may
have additional advantages in correctly identifying the presence of
foreign bodies such as insects or the like on the external
surface.
[0578] In some embodiments of the present invention the light
source may be provided with an internally mounted feedback photo
diode. This feedback photo diode is typically used to monitor the
light output of the light source or sources and adjust the emission
characteristics of the light source e.g. if a decrease in received
light level is measured. However, the internal photo diode could be
used with embodiments of this aspect of the invention by applying
an upper threshold to its received signal and if the received light
level is above the upper threshold (and is not the result of an
increase in light output caused by the controller 5404) this may be
determined to be the result of a foreign body on the external
surface of the optical system 5408.
[0579] An embodiment of the present invention may also be able to
be used with a receiver of a particle detection system. In this
embodiment, the receiver can be fitted with a light emitter such as
that in FIG. 14 and photo diode and be configured to implement the
method as described herein in relation to a light source. With the
receiver, it is clearly advantageous that the transmission of light
within the receiver housing does not interfere with the particle
detection performance of the system. Accordingly, the light source
5502 can be selected such that it emits light outside the reception
band of the receiver, or the receiver can be provided with a band
pass filter which excludes the selected wavelength. Alternatively,
if the light source of the particle detector is set to flash
according to a predetermined pattern with `off periods` between
flashes the foreign body detection function can be performed in
these `off` periods. If foreign body detection in the `off` periods
is to be used the light emitter e.g. emitter 5502, can emit light
in the pass band of the receiver and the main receiver could be
used to detect the presence of foreign bodies on the external
surface of the optical component 5408.
[0580] As noted above, it is important for particle detectors to be
properly installed and commissioned. Correct installation and
commissioning ensures reliable and safe operation of the system. In
this regard several processes that can be used in the set-up and
commissioning of a particle detection system will now be
described.
[0581] For the purposes of clarity, the following process
description will focus on a particle detector as described in
relation to FIG. 2. However, the process may be implemented using
the implementations described in relation to FIG. 3 and other
implementations, which will be apparent to a person skilled in the
relevant art.
[0582] In one embodiment, the process includes two stages,
comprising a commissioning stage and an operation stage. The
commissioning stage is performed on initial installation of the
beam detector, whereas the operation stage is performed some time
after installation.
[0583] A process for commissioning the particle detector is shown
in FIG. 58. A technician or other suitable installer mounts the
light source 32, and receiver 34 and target 36 (which is optional
in other geometries) in appropriate locations spanning an area
requiring monitoring for particles e.g. smoke (step 5801). As
discussed, with the use of a receiver 34 in the form of a video
camera or other suitable device, the process of installation may be
easier and quicker.
[0584] Following installation, in step 5802, the technician
activates the detector by powering the particle detector. Initially
the detector discovers the presence of light sources within its
field of view to monitor. As described elsewhere here and in our
co-pending application the controller identifies the relevant
portion(s) of the detector's field of view that represent light
from the light source 32 and then measures the strength of the
light signal received from the light source 32, in step 5803. This
identification process may be manual, for example with the
technician interfacing a portable computer to the receiver 34,
viewing the image captured by the camera and indicating using a
point and click device or otherwise the relevant portions of the
field of view. The identification process may instead be automatic,
for example with the controller 44 programmed to identify the parts
of the screen illuminated by the light source (e.g. UV and/or
infrared light in the case that UV and/or ultraviolet light sources
are used).
[0585] A detailed description of an exemplary method of target
acquisition and timing discovery can be found elsewhere herein.
[0586] The level of light received from each identified source is
compared to a threshold value to determine if the received light
level is within acceptable limits in step 5804. If the controller
54 receives light from the light source 32 above a preset
threshold, then it causes the particle detector to indicate
acceptable operation (step 5805). Indication of the status of the
system can comprise constantly lighting an LED on the receiver 34,
although other notification mechanisms may be used such as making a
sound and/or transmitting a signal to a PDA or computer in
communication with the controller 44, for viewing by the
technician.
[0587] The detection system will apply alarm and fault logic to
determine either whether the detection system is operating
correctly or whether particles have been detected. The alarm and
fault logic will include alarm criteria based on the intensity of
light received at the receiver. This criteria may be based on raw
intensity measurements, differential or comparative values at
multiple wavelengths or rates of change or other measures known to
those skilled in the art. Typically the criteria can be seen as a
comparison of received data to a threshold level. The inventors
have realised that since Installation and commissioning of the
particle detection system is supervised by the technician and
during commissioning the system is not relied on to provide a
particle detection or life safety function, the usual alarm
thresholds may be largely ignored in the commissioning stage. Thus
the thresholds applied during commissioning stage can be set very
tightly in comparison to one or more of the alarm or fault
thresholds that are applied during the operating stage.
[0588] In a preferred form at least one threshold used in the
commissioning stage will be set substantially above a level that
would cause the particle detector to generate an alarm, take other
action indicating that smoke has been detected or raise a or fault
in the operation phase.
[0589] For example the acceptable minimum level of light received
during the commissioning stage could be set 20% over a light level
that would cause a fault condition during normal operation. Such a
threshold requires an installer to ensure that the initial
alignment of the system is highly accurate, the optical surfaces
are clean and in good condition and that the transmission path
length is not outside acceptable ranges, otherwise the system would
not achieve the relatively stringent light intensity requirements
in place during commissioning.
[0590] If during the commissioning stage the controller 44
determines that the intensity of the light received is below the
preset threshold, then the controller 44 causes the particle
detector to indicate an error (step 5806). This may, for example,
comprise flashing an LED or transmitting a signal to a PDA or
computer of the technician. If the identification of the relevant
portions of the field of view is automatic, the controller 44 may
allow a manual identification process to be completed, following
which steps 5802 to 5804 may be repeated.
[0591] On receipt of the error indication, the technician can
perform the necessary action to rectify the problem. For example
the technician can reposition the light source 32, receiver 34
and/or target 36, for example to reduce the path length between the
light source 32 and the receiver 34. Where a substantial reduction
in path length is required and the initial installation used the
target 36, the technician may remove the target 36 and place the
receiver 34 where the target 36 was previously located, to halve
the path length. The technician could otherwise locate a suitable
mid-point on which to mount the components of the particle
detector.
[0592] The controller 44 may be programmed to complete its part of
the process shown in FIG. 58 automatically on each power up.
Alternatively, the process may be completed only on command, for
example by the pressing of a button associated with the receiver
34, or on receipt of a command through a communication port of the
receiver 34.
[0593] If the commissioning stage has been successfully completed,
the receiver 34 is in condition to start operating. Two embodiments
of this `operation stage` are described below, the first in
relation to FIG. 59 and the second in relation to FIG. 60. During
the operation stage, the receiver 34 measures the intensity of
light received from the light source(s) 32. This data is processed,
and if the signal(s) received indicates smoke is present in the
light path between the light source(s) 32 and the receiver 34, the
controller 44 generates an alarm condition in the particle
detector, and/or communicates a signal to cause another device
(e.g. a fire panel) or system such as an automated evacuation
system, to generate an alarm.
[0594] In the preferred embodiments of the present invention, which
operate a multiple wavelengths, the primary alarm thresholds are
based on a differential measure of received light intensity at more
than one wavelength, e.g. the ratio or difference between received
light intensity at two wavelength, or rates of change of such
measures. A secondary "fallback" threshold can be set on the basis
of the absolute or corrected received light intensity at one or
more wavelengths independently. The detection of correct operation
and fault conditions can also be based on both differential or
absolute received light level.
[0595] Referring to FIG. 59, the controller 44 is programmed to
re-check the signal strength received from the light source 32, or
each light source 32 (if there is more than one) against an
absolute signal strength threshold. This check may be performed
continuously or periodically, for example, once a day, two or more
times a day, or at a lesser frequency, depending on requirements.
The check may also be performed on command, for example on receipt
of a command to check the signal strength received at a
communication port of the receiver 34, or on actuation of a button
provided in association with the receiver 34. If the controller 44
determines in step 5907 that no check is required, the receiver 34
continues to monitor for smoke in the light path.
[0596] If a check is required, then in step 5908 the controller 44
evaluates the signal strength of the light from the light source(s)
32 and in step 5909 compares this to a threshold value. This
threshold value may be the same as that used in step 5803, or may
alternatively be another set value, determined to indicate a
required level of reliability of operation.
[0597] In step 5910, the result of the comparison is evaluated and
if the threshold value for minimum required intensity has not been
exceeded, an error is indicated/generated (step 5911), which error
may be the same as or different to the error indicated in step
5806, depending on the particular implementation. For example, the
error indicated in step 5911 may be an audible signal generated at
the site of the particle detector, and/or at a control station,
such as a security station for a building, and/or a remote
monitoring station by communicating the error over a wired and/or
wireless public and/or proprietary network.
[0598] If the threshold value for minimum required intensity has
been exceeded, then in step 5912, the particle detector indicates
acceptable operation, which may be indicated in the same was as
described for step 5805.
[0599] Referring to FIG. 60, a flow chart of a process that may be
completed by the controller 44 to implement an alternative
operation stage is shown.
[0600] Following commissioning (i.e. following step 5805), the
controller 44 in step 6016 determines if a delay period has
expired. This delay period may, for example, be 24 hours, after
which time it would be expected that the particle detector is
operating in a stable condition. Other non-zero delay periods may
be used in other embodiments. Preferably during the delay period
the detector is not used for essential particle detection purposes,
and is only being monitored for correct operation.
[0601] When the delay period has expired, the controller 44 re-sets
its thresholds (in step 6018). Preferably the new thresholds to be
used are based on either the measured signal strength (or parameter
derived therefrom) that was measured in (optional step) 6015.
Alternatively, it could be based on a measurement(s) made upon the
expiry of the delay (step 6017). The operational threshold
intensity could also have a preset minimum value. Alternatively an
acceptable threshold can be determined by looking at the
performance of the system during the delay period, e.g. by
analysing the variation of received light intensity at one or more
wavelengths during the delay period. For example if the variation
in received light intensity over the period caused by things other
than the impingement of particles of interest into the beam (e.g.
mounting drift, temperature dependent light output variations of
the light sources etc.) is 2% then an acceptable minimum received
light level could be set at 2% below the average received light
level, or at some other level. The operational intensity may be a
function of both the measured intensity at the end of the delay
period and a preset minimum value, for example determined as the
average of the two values. The operational threshold and present
minimum value, if any, may be determined/set independently for each
light path if there is more than one light path.
[0602] Next the controller evaluates the intensity of the light
received from the light source(s) 32 (step 6088A) and compares it
to the new operational threshold in step 609A.
[0603] Steps 600A to 602A may then proceed as described herein
above in relation to FIG. 59, using the operational threshold value
determined in step 689A.
[0604] Where there are multiple light sources and/or multiple light
paths from a single light source, the error may be indicated when
the intensity of light received along any one of the monitored
light paths falls below the threshold. Alternatively, there may be
different levels of error condition, with one level indicating when
light along one of the light paths falls below the threshold and
another level indicating when light alone more than one or all
paths falls below the threshold. The threshold may be different for
each light path, reflecting for example differences in the
intensity of light generated by the light source 32 for that
path.
[0605] In the foregoing description, reference has been made to
individual light paths from the light source(s) 32 to the receiver
34. Those skilled in the relevant art will appreciate that light
may be reflected off various structures, such as a ceiling, and as
a result there may be more than one light path between a light
source and a particular point on a receiver. Implementations where
light from a source is received by the receiver by multiple paths
and where light from one light source is reflected onto the part of
the receiver receiving light from another light source are intended
to be within the scope of the present invention.
[0606] Turning again to FIG. 57, in an installation such as this,
the difference in the intensity of light arriving at the receiver
5702 from the transmitters 5704, 5706, 5708 can be adjusted in an
embodiment of a further aspect of the invention by applying an
optical attenuator to the optical path of each transmitter in the
system, or at least those transmitters in the system which are
located at a distance likely to cause saturation of the receiver
5702. FIG. 61 shows exemplary housing which may be used to
implement this mechanism. FIG. 61 shows a cross sectional view
through a transmitter housing 6100. Within the housing there is
located a light source such as an LED 6102. This is connected to
appropriate circuitry (not shown) and is used to generate a beam of
light for use in particle detection. The light emitted by the light
source 6102 may pass through one or more optical elements 6104 for
focusing the beam into an appropriate shape eg a narrowly diverging
column or broad divergent beam, or some other shape as discussed
herein. The transmitter 6100 additional includes one or more
optical attenuators 6108 for attenuating the beam emitted from the
transmitter 6100. The level of attenuation can be selected and set
at an appropriate level for the separation between the transmitter
and its corresponding receiver by using one or more filters 6108
having suitable ???? characteristics. Multiple filtering elements
can be added in series to achieve the appropriate attenuation
level. An example of a system with multiple filters is shown in
FIG. 62. In FIG. 62 like components have been numbered to
correspond to FIG. 61. In a preferred embodiment the housing 6106
of the transmitter 6100 can be configured to have structures 6112
for receiving the filters 6108 (and 6110) in the appropriate
position. Most preferably, the receiving mechanism enables
selectable filters to be attached and removed by the installer
during commissioning of the system. For example, the housing can
include a plurality of grooves, e.g. grooves 6112, which are each
adapted to receive an individual filter element.
[0607] FIG. 63 shows three exemplary filter elements which may be
used with an embodiment of the present invention such as that
illustrated in FIG. 61 or 62. The filters 6300, 6301, 6302 are
preferably neutral density filters and can be made of an
attenuating material, such as a plastic film. Attenuators for
different distances can be made by increasing the level of
absorption of the material e.g. by changing material properties or
increasing thickness of the material.
[0608] Preferably each filter has indicia indicating the strength
of the filter. For example, an indication of a preferred distance
or distance range between the transmitter and receiver can be
printed, embossed or otherwise displayed on the filter.
Alternatively, a fractional attenuation level can be displayed.
This information displayed on the filters can be used by the
installers to determine the appropriate filter or group of filters
to use with a transmitter for the particular system geometry being
installed.
[0609] An alternative (or complimentary) embodiment of this aspect
of the invention will now be described. In this embodiment the
system is adapted to enable the receiver to avoid saturation
without the use of a filter, although filters could be used with
this embodiment if necessary. FIG. 64 is a timing diagram
illustrating a second solution to the abovementioned problem
according to an aspect of the present invention.
[0610] In this aspect of the invention a transmitter can be
configured to emit a sequence of pulses of differing intensity and
to repeat this sequence during operation. The receiver can then
determine which of the received pulses falls within an acceptable
light level at the receiver and from that time forward choose to
receive only those pulses which have an acceptable light level.
[0611] Turning now to FIG. 64 the uppermost plot 6400 is a timing
diagram showing the transmission power of a sequence of pulses
emitted by a transmitter over time. The lower plot shows the
reception state of the receiver. In an initial time period t.sub.1
the transmitter cycles through a sequence of transmission pulses
6404, 6406 and 6408 of progressively increasing transmission power.
This sequence is repeated in time periods t.sub.2 and t.sub.3 and
continuously thereafter. In the first time period t.sub.1 the
receiver does not know which transmission pulse is going to be at
the appropriate level so as not to saturate the receiver but also
be high enough to have adequate signal to noise ratio. Therefore,
for time period t.sub.1 the receiver is continuously in an "on"
state and is able to receive each of the transmitted pulses 6404,
6406 and 6408. On the basis of measured intensity of the three
received pulses the receiver can determine which pulse should be
received from then on. In this case, the pulse 6408 is determined
to have the correct intensity and the receiver is configured to be
activated at times 6410 and 6412 which correspond to the time of
transmission of pulse 6408 in the successive transmission periods
T2 and T3.
[0612] As described above the receiver and transmitter are
generally not in communication with each other, and the transmitter
will continue to emit three different level pulses throughout its
operation. Alternatively, in an embodiment where the receiver may
communicate back to the transmitter, the receiver can signal to the
transmitter which of the pulses to continue emitting and which of
the pulses to omit. Such a system will reduce the power consumption
of the transmitter as fewer pulses will be emitted.
[0613] The initial period of monitoring the various transmission
pulses may be extended beyond the single transmission time period
as it may be necessary for the receiver to discover the pattern of
illumination of the transmitter over several transmission time
periods.
[0614] In a third solution for ameliorating or addressing this
problem a further aspect of the present invention uses electronic
means to control the transmission power of the transmitter. In this
example a DIP switch can be incorporated into the transmitter which
during installation is set to the appropriate transmission level by
the installer. The setting on the DIP switch can be chosen to
either reduce the current through the LED and thus dim the LED or
reduce the duration of the pulse "on period" to avoid saturation of
the receiver. In this case it may be advantageous to have an
installation mode in which the transmitter emits light at differing
power levels initially. During this period the receiver can
determine the appropriate transmission level and indicate to the
installer the appropriate DIP switch setting (or settings) to be
made to set the transmission level to the most preferable value.
For example, the receiver may be provided with a display or other
interface that can be used to indicate the DIP switch settings for
the transmitter. It should also be appreciated that in a system
with a plurality of transmitters any process can be repeated for
each transmitter.
[0615] In a further embodiment of this aspect of the present
invention a system having multiple transmitters may include
transmitters of different types in it. Each transmitter type can be
optimised for use at a particular distance or range of distances
and in this case is up to the installer to select what type of
transmitter should be installed.
[0616] FIG. 65 illustrates an embodiment of a particle detection
system 6500 being tested using a test filter according to an
embodiment of another aspect of the present invention. The particle
detection system 6500 includes a light source 6502 a light receiver
6504. The light source 6502 generates one or more beams of light
including light in a first wavelength band 6506 which is in a
wavelength band centred at .lamda.1 and a second wavelength band
6508 centred at .lamda.2. Preferably, .lamda.1 is a shorter
wavelength band, for example in the ultraviolet part of the
electromagnetic spectrum, and .lamda.2 is a longer wavelength band
e.g. centred in the near infrared. The light beams 6506 and 6508
pass through a test filter 6510 which mimics the effect of smoke on
the beam by alternating the beams 6506, 6508. The operation of the
receiver 6504 can then be checked to determine if its behaviour is
correct given the extent of beam attenuation being caused by test
filter 6510. Because the light emitted by light source 6502
includes light in two wavelength bands .lamda.1 and .lamda.2 the
filter 6510 needs absorption characteristics which treat these two
wavelength bands in an appropriate manner. In a preferred form of
particle detector 6500, as described above, a differential measure
of light intensity in the two wavelength bands .lamda.1 and
.lamda.2 (e.g. ratio of measured intensities at each wavelength or
a rate of change of these values etc.) is used to determine the
presence of particles of a predetermined size range within the
beams 6506 and 6508. Most preferably, if the ratio of the received
light intensities varies in a predetermined manner then a particle
detection event may be indicated. Accordingly, in most cases the
test filter 6510 does not attenuate both wavelength bands evenly
but must provide a differential attenuation in the two wavelength
bands .lamda.1 and .lamda.2 to mimic the effect of smoke. In this
example, the test filter 6510 absorbs the shorter wavelength
.lamda.1 significantly more than the longer wavelength .lamda.2.
For example, the test filter can absorb twice as much of the light
in .lamda.1 as it does in .lamda.2, which may be determined to look
like a particular type of particle.
[0617] Thus the test filter characteristics are chosen to set both
the ratio of light transmitted (or attenuated) in different
wavelength bands and to also to vary the absolute level of light
transmitted (attenuated) by the test filter. These two variables
can be adapted to produce a suitable test filter to mimic different
smoke or particle types as well as different smoke or particle
densities.
[0618] FIG. 66 illustrates a first exemplary test filter comprising
three filter elements 6512, 6514 and 6516. The test filter 6510 is
a generally sheet like material formed by three layers of filter
material. In this example, the first two filter elements 6512 and
6514 attenuate light in wavelength band .lamda.1 and the third
filter element 6516 absorbs light in wavelength band .lamda.2. In
this example each of the filter elements 6512 to 6516 making up the
test filter 6510 are configured to provide the same amount of
attenuation of light passing through it. Accordingly, the test
filter 6510 attenuates light in wavelength band .lamda.1 twice as
strongly as it does light in wavelength band .lamda.2.
[0619] FIG. 67 illustrates a transmission spectrum for the test
filter 6570. As can be seen, the test filter transmits
substantially all of the light outside wavelength bands .lamda.1
and .lamda.2 but attenuates about twice as much of the light in
wavelength band .lamda.1 as it does light in wavelength band
.lamda.2. In other embodiments transmission outside wavelength
bands .lamda.1 and .lamda.2 can be any level and need not be
uniform over all wavelengths.
[0620] The absorption characteristics described above can be
achieved in a wide variety of ways. FIGS. 68 to 75 illustrate a
range of these techniques. Others may be apparent to those skilled
in the art.
[0621] FIG. 68 illustrates a filter element. The filter element has
a front face 6802 to which is adhered a plurality of particles
having a particle size distribution substantially equal to the
particles to be detected using the particle detector to be tested
using the filter element. Such particles can be manufactured using
a number of well known processes or selected by filtration and
separation from powder such as aluminium oxide. FIG. 69B
illustrates a variant on this mechanism. The filter element 6900 of
FIG. 15B includes particles similar to those used in the embodiment
of FIG. 68, but distributed through the bulk of the filter
element.
[0622] FIG. 70 shows a filter element 7000 on which one or both
surfaces has had a surface treatment to cause defects on the
surface of the material. Surface defects can be generated for
example by mechanical abrasion, particle blasting, chemical or
laser etching or the like. Alternatively defects may be created
through the bulk of the filter element in FIG. 70 using for example
3D laser etching.
[0623] FIGS. 71 and 72 illustrate further surface treatments that
can be performed on filter element 7100, 7200 to achieve
predetermined attenuation characteristics. In these examples the
filter element is formed of a substantially transparent material
and is modified by the application of surface printing. For
example, an inkjet or laser printer can be used to print a pattern
on one or both surfaces of the filter element sheet. Preferably, a
pattern of dots is printed over the entire surface of the filter
element. Most preferably the dots of a uniform size are printed at
a predetermined separation which is determined by the level of
attenuation to be achieved by the filter element. FIGS. 71 and 72
are substantially identical apart from the number of dots printed
on the filter element. As can be seen, FIG. 71 has far less dots
printed on it than FIG. 72 and accordingly will be less absorptive
than the filter element of FIG. 15E.
[0624] Obviously other patterns can be used to achieve a
predetermined attenuation.
[0625] FIG. 73 illustrates a printing pattern which can be
implemented on a surface of a filter element 7300. This filter
element 7300 is printed with two colour printing process and
includes a dot pattern which has dots of a first colour 7304 and
dots of a second colour 7306. As can be seen there are more dots of
colour 6804 than of colour 6806 and accordingly the filter element
will attenuate more light in one wavelength band than the other.
Alternatively, a dot pattern in one colour, could be printed on one
side of the filter element and a dot pattern on the other side can
be printed in the second colour.
[0626] FIG. 74 illustrates a test filter having a more complex
structure. This test filter element 7408 is made of five layers
7410 to 7418. Four of the layers 7410 to 7416 attenuate light in
wavelength band .lamda.1 but are transmissive to all other
wavelength bands, and the last layer 6818 absorbs at wavelength
band .lamda.2.
[0627] FIG. 75 illustrates another test filter. This test filter
has a central portion 7420 which has characteristics chosen to
achieve a predetermined attenuation of light in wavelength bands
.lamda.1 and .lamda.2 but it is laminated with transparent layer
7422 and 7424 to protect the attenuating layers forming the core
7420. This can be particularly advantageous where the attenuating
layers use a surface treatment which may be damaged by contact with
other objects or substances.
[0628] In another embodiment one or both of the surfaces of the
test filter can be treated with a plurality of thin films to create
a predetermined wavelength selective attenuation profile. Moreover,
the filter elements can be reflective rather than absorptive, to
achieve the desired attenuation profile.
[0629] FIG. 76 illustrates a beam detector 7600 which includes a
transmitter or light source 7602 and receiver 7604. The transmitter
7602 includes one or more light emitters 7606 which are adapted to
generate one or more beams of light 7608. At least a portion of the
one or more beams are received by the receiver 7604. Preferably,
the light emitter 7606 is adapted to simultaneously generate light
within two wavelength bands centered at different wavelengths
.lamda..sub.1 and .lamda..sub.2 hereinafter termed "wavelength
bands .lamda..sub.1 and .lamda..sub.2" for transmission to the
receiver 7604. The receiver 7604 includes a light sensor 7610 which
is adapted to output a signal representing the received light
intensity at a plurality of positions on its surface in the two
wavelength bands. The output in the two wavelength bands is passed
to a controller 7612 which performs analysis on the output of the
light receiver 7604 and applies alarm and/or fault logic to
determine whether an action needs to be performed in response to
the received signal or signals. The receiver 7604 may additionally
include optical system 7614 for forming an image or otherwise
controlling the received beam 7608.
[0630] In an embodiment of the present invention where the light
emitter 7606 simultaneously emits in two wavelength bands
.lamda..sub.1 and .lamda..sub.2 the sensor 7610 of the receiver
7604 is preferably adapted to simultaneously and distinguishably
receive light in each of the wavelength bands. In order to achieve
this aim, the receiver 7604 can be provided with wavelength
selective component which is adapted to split light in wavelength
band .lamda..sub.1 from light and wavelength band .lamda..sub.2 and
differentially direct them to the sensor 7610 in a manner which
enables the two wavelength components to be separately
measured.
[0631] FIG. 77 illustrates a first example of a receiver 7750 which
enables this technique to be performed. The receiver 7750 includes
a window 7752 through which a light beam 7754 enters the receiver
7750. The window 7752 may be a flat piece of glass or similar or
alternatively may be part of an optical arrangement (e.g. a lens or
series of lenses) adapted to form an image on or near the light
receiver. The receiver 7750 includes a sensor 7756 which includes a
plurality of sensor elements 7758. A wavelength selective component
7760 is mounted adjacent the front face of the light sensor 7756
and comprises for example, a mosaic dye filter. The dye filter 7760
includes a plurality of cells 7762 and 7764. The cells 7762 are
adapted to be transmissive in a first wavelength band .lamda..sub.1
and the cells 7764 are adapted to be transmissive in a second
wavelength band .lamda..sub.2. The combination of mosaic dye filter
7760 and light sensor array 7756 enables a first group of sensor
elements or pixels of the sensor 7756 to receive light in the first
wavelength band whilst other pixels of the sensor array 7756
simultaneously receive and record light intensity use in a second
wavelength band .lamda..sub.2.
[0632] The controller can then be configured to separate the
intensity values in one group (i.e. relating to one wavelength
band) from the other, e.g. the outputs of the sensor elements can
be selectively "read out" to obtain the two wavelength band
signals.
[0633] FIG. 78 shows an alternative embodiment which achieves a
similar result. In this embodiment the receiver 7800 is similar to
that of FIG. 77 in that it includes an optical component 7802 which
may comprise a window or focusing optics through which light enters
the receiver housing 7804. After passing through the optical
component 7802 the beam enters a wavelength selective prism 7806
which is adapted to divert light in different directions depending
upon the wavelength of the incident light. Accordingly, light in
wavelength band .lamda..sub.1 is transmitted into a first beam 7808
whereas light in wavelength band .lamda..sub.2 is transmitted in a
second beam 7810. The beam in wavelength band .lamda..sub.1 falls
on a first sensor array 7812 and light in the second wavelength
band .lamda..sub.2 falls on a second sensor array 7814. As
previously described in relation to earlier embodiments, the sensor
arrays 7812 and 7814 are adapted to record the intensity of light
at a plurality of points on its surface simultaneously.
[0634] FIG. 79 shows a second embodiment using a prism to split a
beam into its wavelength components. In this embodiment the
receiver 7820 includes a single sensor array 7822 adapted to
receive light via an optical component 7824 and a beam splitting
component 7826. The beam splitting component is adapted to split
light in a first wavelength band from light in a second wavelength
band and to direct these in different directions. This embodiment
differs to that of FIG. 78 in that rather than forming images in
each of the wavelength bands .lamda..sub.1 and .lamda..sub.2 on
separate sensor arrays the beam splitting component 7826 is mounted
very close to the sensor array 7822. In this way, as the beam
splitting takes place very close to the surface of the sensor array
7822. Effectively, this provides a separate wavelength selective
beam splitter for a subset of pixels of the sensor element
7822.
[0635] FIG. 80 illustrates a further embodiment of the present
invention. This embodiment illustrates a light receiver 7850
including a housing 7852 in which is mounted a sensor element 7854.
Light enters the housing through an optical system 7856 and is
transmitted to the light sensor 7854. In this embodiment, the
sensor 7854 is a multi-layered sensor and includes n sensor layers
7854.1, 7854.2 through 7854.n. Each sensor layer 7854.1 through
7854.n is adapted to receive light at a different energy. This
energy separation is achieved by taking advantage of the phenomenon
that different energy photons will penetrate at different depths
into the sensor device 7854. In this case the sensor device can be
a silicon light sensing element. In each layer of the sensor 7854 a
spatially distinct measure of light intensity can be determined at
its corresponding wavelength.
[0636] In each of the embodiments described above the signals at a
plurality of wavelengths can be processed in accordance with the
aforementioned methods to produce a particle detection or fault
condition output.
[0637] It should be appreciated that although the preferred
embodiments were described in connection with the two wavelength
system, three or more wavelengths may be used in some
embodiments.
[0638] FIGS. 81 and 82 show one embodiment of the present invention
that includes a transmitter 8101 for emitting at least one beam of
light 8102, and a receiver 8103 for receiving the beam. The
receiver 8103 has a light sensor having multiple photosensitive
elements 8104. An example of a suitable receiver is a video imager
whose sensors are arranged into a matrix of pixels. Each sensor
element produces an electric signal that is related e.g.
proportionally, to the intensity of the light detected by that
sensor.
[0639] In FIG. 81, the transmitter 8101 is shown as being
positioned opposite the receiver 8103 across a monitored space
8105. However it should be understood that the transmitter 8101 can
be otherwise located (i.e. not directly aiming the emitted beam
toward the receiver 8103) as long as the emitted beam 8102 crosses
the monitored space 8105. The emitted beam 8102 can be directed
toward the receiver 8103 by an arrangement such as an optical
reflector.
[0640] A diffusing means 8106 is provided in the path of the
emitted beam 8102, so as to produce a deliberately diffused image
of the beam on the receiver's sensor 8107A. Signals from the sensor
elements 8104 are transmitted to a controller 8108, such as a
processor.
[0641] The controller 8108 combines the signals from at least some
of the sensor elements e.g. only those on which the beam falls,
group 8109 to determine the intensity of the received beam 8107A.
Each sensor element in the CCD 8103 can have a different inherent
noise level, and a different light conversion efficiency.
Therefore, in its calculations, the controller 8108 takes into
account information regarding the sensor elements 8109A that are
initially in alignment with the beam 8107A. Based on the determined
intensity, the controller 8108 applies alarm logic and decides
whether any action, such as signalling an alarm, or dispatching an
alert or a message to an administrator or another user, should be
taken. In previously described systems, the decision has been made
based on whether the determined intensity is lower than a threshold
value that corresponds to a presence of smoke particles.
[0642] In FIG. 82, the position of the transmitter 8101 is shown as
being slightly removed from its position as shown in FIG. 81. This
change results in a change in the position of the diffused beam
image 8107B, relative to the receiver 8103. Some of the sensor
elements onto which the diffused beam 8107B is incident are outside
the initial subgroup of sensor elements 8109 whose signals are
initially read by the controller 8108. The controller 8108 is
adapted to track the position of the image of the beam across the
surface of the sensor 8103 and consequently integrates the received
light over sensors in a new region 8109A. As would be appreciated
the group of sensors within the region 8109A is different to that
which was originally used as group 8109, but the two groups (8109,
8109A) include the same number of sensors.
[0643] The sensor elements in the new region 8109A theoretically
can have a different inherent signal error than the sensor elements
in the original region 8109. However, this difference is not
significant. In this example the average inherent noise level of
the four newly integrated sensor elements will be about the same as
that of the four sensor elements that are no longer used. Moreover,
the spacing (i.e. number and size of gaps) between sensor elements
remains substantially constant and thus no additional light is lost
in the gaps between sensors elements.
[0644] This can be contrasted to the case of a sharply focused beam
image where the error related to the received beam strength will
change dramatically as the sharply focused beam moves from one
sensor element to the next because the two sensors have different
light conversion efficiencies and the difference is not ameliorated
by averaging (as in the case of a more diffused beam image).
Further, as the focused beam moves from one sensor element to the
next it will scan past the space between the sensor elements, and
there will be an intervening period where a substantial amount of
the beam power will be lost in the space between the sensors. As
described above, these problems are mitigated by use of a defocused
image.
[0645] The following paragraphs describe examples of how the optics
(i.e. imaging system) used in the receiver can be arranged so as to
produce a deliberately defocused target. In this specification, the
term `diffusing means` should be read broadly to refer to any
arrangement or component that produces a diffused image of the beam
on the sensor.
[0646] In the embodiment illustrated in FIG. 83, the diffusing
means 8301 includes a focusing lens 8302 that is located in the
emitted beam's path.
[0647] The focusing lens 8302 has an associated focal point 8304.
The emitted beam 8303 is either transmitted directly by the
transmitter (not shown) toward the lens 8302 or toward a reflector
(not shown) that reflects the beam toward the lens 8302. In this
embodiment, the relative positions of the lens 8302 and the sensor
8305 are such that the sensor is displaced from the position where
the focused beam image 8306 is located. The sensors 8305 therefore
receive a beam image that is deliberately slightly defocused. The
amount of focus and the amount of diffusion are controlled so that
the signal to noise ratio can be obtained (achieved with a more
tightly focused beam) while achieving a system that is relatively
stable (achieved with a diffused or blurred image) even when there
are movements in the system.
[0648] In a further embodiment (FIG. 84), the receiver 8310
includes a focusing lens 8311. The light sensor 8312 is placed at
the spot where the focused image is located. The diffusing means in
this embodiment includes a diffuser 8313 that is placed somewhere
between the lens 8311 and the light sensor 8312 (e.g. directly over
the sensors). The received image is therefore deliberately blurred.
The diffuser 8313 can be a piece of ground or etched glass or
simply comprise an etched face on the sensor itself.
[0649] In some cases, the diffusing means 8313 can be located
somewhere in the emitted beam's path to the sensor 8312.
[0650] In some embodiments the transmitter may output a light beam
having components in two (or more) wavelength bands, for example
infrared (IR) and ultraviolet (UV) light bands, both emitted along
a substantially collinear path. The two wavelengths are chosen such
that they display different behaviour in the presence of particles
to be detected, e.g. smoke particles. In this way the relative
change in the received light at the two (or more) wavelengths can
be used to give an indication of what has caused attenuation of the
beam.
[0651] In some embodiments, the receiver may receive multiple
beams, or multiple transmitters may emit beams to be received. The
multiple beams are used together for the purpose of smoke detection
in the monitored space. As with the previous embodiments, the
sensors receive the beams and send signals to the controller. The
controller analyses the signals, and determines which portion of
the signals contains information most strongly related to the
respective beams. At the conclusion of this decision process, the
controller will have selected two portions of signals that are
produced by respective individual sensors or groups of sensors, so
the selected signal can most reliably be used to measure the
intensity of beams. One way of selecting the sensors whose data can
be most reliably used is to view the image generated by the
receiver at the time of commissioning the smoke detector and
selecting the appropriate sensors.
[0652] A further mechanism of ensuring that the calculated received
beam intensity is as close to the actual intensity of the received
beam as possible, may be performed by the controller. The
controller may decide whether to use the value corresponding to a
certain sensor element, according to that element's contribution to
the overall image strength. For example, from the sensor element
outputs, the controller can determine a `centre-of-signal` position
of the beam. The centre-of-signal position is analogous to the
centre of mass position, except that instead of mass, it is the
signal value contributed by each pixel (i.e. sensor element) that
is used in the calculation. For example, the following equation may
be used:
Centre-of-signal position vector={sum of (position vector of each
pixel)*(value of each pixel)}/{sum of values from all the
pixels}.
[0653] After the centre-of-signal position is determined, the
controller may weight the signal contributed to the received beam
intensity value by each sensor element (i.e. corresponding to the
electrical signal generated by each sensor) according to the
distance between that sensor element and the centre-of-signal
position. In this way, the controller determines the sensor
elements whose signals best represent the target image and that are
least likely to be dropped from subsequent measurements due to
drift in the beam image's position on the sensor.
[0654] FIG. 85 illustrates an embodiment of a further aspect of the
present invention. In this embodiment, the particle detection
system 8500 includes a transmitter 8502 and a receiver 8504. The
transmitter 8502 includes a light source or light sources adapted
to emit light including light into wavelength bands .lamda..sub.1
and .lamda..sub.2. The light source 8502 can include a plurality of
light emitting elements each adapted to emit in a different
wavelength band, or a wide band light source. The transmitter 8502
can additionally include one or more optical components e.g. 8506
for forming a beam of light of desired beam profile or dispersion
characteristics. The receiver 8504 can also include a light
directing or image forming optics 8508 which are adapted to form an
image of the beam on a sensor array 8510 of the receiver 8504. In
order to minimise the interference of ambient light with the
receiver 8504 the receiver 8504 is also provided with a multiple
passband filter arrangement 8512. For example, the multiple
passband filter can be an interference filter which is arranged to
selectively transmit light of the first passband and second
passband corresponding to emission bands of the light source 8502.
Most preferably, the filter arrangement 8512 is a multiple passband
interference filter which has a passband at a long wavelength and
one or more harmonics of that wavelength. In such an embodiment,
the light source 8502 must be configured to emit light at similarly
related harmonics. For example, a single interference filter can be
designed to transmit substantially all light at 800 nanometres and
also at 400 nanometres while blocking a large majority of light at
other wavelengths. When using such a filter the light source can be
adapted to emit at 800 nanometres and 400 nanometres.
[0655] In a further embodiment of the present invention the filter
arrangement 8512 can include more than one interference filter or
dye filter or other similar type of filter used in parallel. For
example, two, or more filters, corresponding to the number of
wavelength bands in which the system is configured to operate, may
be placed in side by side relationship in the imaging path of the
receiver. FIGS. 86 to 89 illustrate examples of such filter
arrangements. In this regard, the filter arrangements of FIGS. 86
to 89 include portions adapted to transmit light in a first
passband indicated by reference symbol 8602 and shaded white, and
alternate portions shaded grey and indicated with reference numeral
8604, which are adapted to transmit light in a second passband.
FIG. 88 is adapted for use in a four wave length system and
therefore additionally includes portions indicated with reference
numeral 8606 and 8608 which are adapted to transmit light in a
third and fourth wavelength bands. In each of the filter
arrangements, the surface of the filter is approximately equally
divided between the different wavelength components and thus
transmit substantially even amounts of light in each wavelength
band to the receiver. Such an arrangement has a disadvantage
compared to the abovementioned multiple passband filter arrangement
in that the effective receiver lens diameter is reduced e.g. by
approximately one half for each wavelength in FIGS. 86, 87 and 89,
thus reducing the effective signal strength. However this is to
some extent compensated for by the fact that the light source LED
need not be at harmonics of each other but can be selected on other
merits such as cost of goods. Moreover, the filters used in such an
arrangement may be of lower cost and not require such accurate
wavelengths centring and therefore will not be so sensitive to
variations in transmitter output with temperature fluctuation.
[0656] FIG. 90 illustrates a schematic representation of a fire
alarm system in which an embodiment of the present invention can be
used. The fire alarm system 9000 includes a fire panel 9010 to
which is connected a fire alarm loop 9012. The fire alarm loop 9012
delivers power and communication from the fire panel to various
pieces of fire alarm equipment attached to the system 9000. For
example, the fire alarm loop 9012 can be used to communicate with,
and power, one or more point detectors 9014 and alarm sirens 9016.
It can also be used to communicate with one or more aspirated
particle detectors such as detector 9018. Additionally, a beam
detector system 9020 can also be attached to the fire alarm loop
9012. In the present invention the beam detector system 9020 can be
of the type described above in relation to any of the embodiments
herein and include a receiver 9022 at a first end and at a
transmitter 9024 located remotely to the receiver. Preferably, the
transmitter 9024 is a battery powered device and does not require
power to be drawn from the fire alarm loop 9012. Alternatively, it
can be powered e.g. off separate mains power or loop. The receiver
9022 is connected to the fire alarm loop 9012 and draws power from
the loop and communicates with the fire panel 9010 via the loop.
The means of communication will be known to those skilled in the
art and allow the beam detector 9020 to indicate a fire or fault
condition or other condition back to the fire panel 9010.
[0657] The present inventors have realised that since smoke
detectors do not need to respond instantaneously, acceptable
average power consumption could be obtained by activating the video
capture and/or video processing subsystems of the smoke detector
intermittently, interspersed with periods when processing and
capture is suspended. Thus the system can enter a "freeze" state in
which it is designed to consume very little or no power.
[0658] A first way of achieving this solution is to provide the
video processing subsystem of the particle detector with a simple
timer unit which operates to activate the video capture and
processing subsystems intermittently.
[0659] However, in the preferred form of the system the transmitter
9024 is not powered from the loop or other mains power, but is
battery powered and is preferably not connected to the receiver
9022 or in high speed communication with it. Consequently the
transmitter 9024 must emit light at only very low duty cycle to
conserve power. In such a system the timing of each transmitted
burst of light may neither, be controlled by the receiver or
synchronised with any other receiver which may also be
communicating with the same transmitter 9022.
[0660] Furthermore, during the video processor "freeze" period the
receiver 9022 may still be required to manage other functions such
as servicing polls from the fire alarm loop, or blinking display
LEDs or the like. Therefore, using a simple timer mechanism to
activate the system processor and awake it from its "freeze" state
is not the preferred solution to this problem.
[0661] In a preferred form of the present invention the receiver
9022 employs a secondary processor, having much lower power
consumption than primary processor, which is used to activate the
primary processor and to deal with other functions that must
continue without interruption when the primary processor is in its
"freeze" state.
[0662] FIG. 91 illustrates a schematic block diagram of a receiver
9100 embodying this aspect of the present invention.
[0663] The receiver 9100 includes an imaging chip 9102, e.g., a
CMOS sensor manufactured by Aptina Inc, part number MT9V034, for
receiving optical signals from a transmitter 9024.
[0664] It may optionally include an optical system 9104 e.g. a
focusing lens, such as a standard 4.5 mm, f1.4 c-mount lens, for
focusing the received electro magnetic radiation onto the imaging
chip in the desired manner.
[0665] The imaging chip 9102 is in data communication with a
controller 9106 which preferably is an Actel M1AGL600-V2 field
programmable gate array (FPGA), and an associated memory 9108
including a PC28F256P33 flash ROM for program storage, two
IS61LV51216 high-speed RAMs for image storage and two CY621777DV30L
RAMs for program execution and data storage. The controller's
function is to control the image chip 9102 and perform the required
sequence of data manipulations to carry out the functions required
by the detection system. The control means has sundry additional
components as required for correct operation as well understood by
those skilled in digital electronics design.
[0666] A second processor 9112 is also provided. This processor
9112 can be a Texas Instruments MSP430F2122 microcontroller or
similar, and performs functions such as checking the health of the
control means and if needed signalling fault to external monitoring
equipment if the control means fails or if the control means, for
any other reason, cannot perform its required tasks. It is also
responsible for the timely control of power to the control and
imaging means in order to minimize power consumption. This is
performed by processor 9112 de-activating the main processor 9106
when it is not needed and waking it up intermittently when it is
required.
[0667] Processor 9112 is also in data communication with interface
means 9114 such as a display or user interface and is also
connected to the fire alarm loop to enable data communication with
other equipment connected to the fire alarm loop e.g. a fire
panel.
[0668] In the preferred embodiment the interface 9114 means is used
to notify external monitoring equipment if an alarm or fault
condition exists. If it is determined by the receiver that a fault
exists, the interface means notifies this to the monitoring
equipment (e.g. fire panel 9010 of FIG. 3) by opening a switch
thereby interrupting the current flow out of the aforementioned
monitoring equipment. In the preferred embodiment the switch is a
solid state arrangement employing MOSFET transistors which has the
benefit of being activated and deactivated with very low power
consumption. If it is determined by the receiver that an alarm
condition exists, the interface means notifies this to the
monitoring equipment by drawing current in excess of a
predetermined threshold value from the monitoring equipment. In the
preferred embodiment the excess current draw is achieved by the
positioning of a bipolar-transistor, current-limited shunt across
the interface wires from the monitoring equipment. A total current
draw of approximately 50 mA is used to signal the alarm condition.
In the preferred embodiment, power for normal operation is drawn
from the connecting wires to the monitoring equipment at a constant
current of 3 mA under non-alarm conditions.
[0669] In the preferred embodiment of the present invention the
transmitter 9024 includes a controller to control its illumination
pattern, illumination time, sequence and intensity for each of the
light sources, e.g. infrared and ultra-violet. For example this
could be a Texas Instruments MSP430F2122 microcontroller. The
microcontroller also detects activation of the device when first
installed. In the preferred embodiment of the transmitter, the
power source is a Lithium Thionyl Chloride battery.
[0670] In a preferred form of the present invention, during
commissioning of the system the main processor 9106 can be
programmed to discover the illumination pattern of each of the
light sources (eg light source 9024 of FIG. 3) and over a period of
preferably several minutes e.g. 10 minutes, determine its
activation pattern. This process can be repeated for all light
sources associated with the receiver. The low power processor 9112
can use the discovered light source sequencing information to
activate the primary processor 9106 at the correct time.
[0671] As will be appreciated, by using a system of this structure
the function of the system which must operate at all times can be
controlled by the very low power consumption processor 9112 whilst
the highly intensive processing can be performed intermittently by
the main video processor 9106, and in doing so the average power
can be maintained at a relatively low level.
[0672] The inventors have determined that, there are various and
often competing constraints associated with practical embodiments
that must be dealt with when choosing the illumination pattern of
the transmitter and corresponding receiver operation to accurately
acquire and track a transmitter output. For example, in some
systems it is desirable to use the rate of change of attenuation to
distinguish fault conditions from particulate detection events.
This complicates the use of long integration times discussed in the
background. The preferred embodiment uses an integration period of
10 seconds for normal measurements, and a shorter integration
period of one second is used for rate of change based fault
detection.
[0673] Another constraint on system performance is the scene
lighting level. For a practical system it is usually necessary to
assume the scene may be lit by sunlight for at least part of its
operational life. There may also be limitations on the ability to
use wavelength selective filters on the camera (e.g. at least cost
limitations). Therefore. it will be necessary to use short
exposures to avoid saturation, and still leave sufficient head room
for the signal. In preferred implementations of the system the
exposure duration is 100 .mu.s, but the optimum value will depend
on the choice of sensor, filter, lens, worst case scene lighting
and the amount of headroom required for the signal.
[0674] A means of synchronising the receiver with the transmitter
is also required. It is preferable to achieve this without the use
of additional hardware such as a radio system. Instead in one
desirable implementation the synchronisation is performed optically
using the same imaging and processing hardware that is used for
particle detection. However, as a person skilled in the art will
appreciate, the use of the same hardware for particle detection as
for synchronisation links two concerns within the system, an
thereby imposes a further constraint on the possible solutions.
[0675] Another constraint within the system is due to the presence
of noise. The prime noise sources in the system are camera shot
noise and noise from light variations in the scene. Dark noise is
generally not a significant contribution for systems that must deal
with full sunlight. Scene noise is dealt with very effectively by
the background subtraction method described in our earlier patent
applications. Shot noise cannot be totally removed, as it is
fundamental to the quantum detection process. However, shot noise
can be reduced by reducing exposure time, and also by summing fewer
exposures. In the preferred embodiment, substantially all
transmitter power is put into very brief flashes, with a repetition
rate that still allows an adequate system response time.
[0676] For example, a flash rate of 1 per second will satisfy the
response time requirement, and a flash duration of less than 1
.mu.s and an exposure time of 2 .mu.s could (in principle) be used.
In practice this would be very difficult to synchronise. In
addition, the transmitter LEDs would need to handle a very high
peak current to deliver the energy in such a short time, which in
turn would increase cost. Another limitation is the dynamic range
of the sensor. Putting all the power into one flash per second
could result in saturation in the sensor.
[0677] In consideration of the above factors the preferred
embodiment uses an exposure of 100 .mu.s, a flash duration of 50
.mu.s, and a period of 9000 ms. An integration length of 3 samples
is used for rate of change based fault detection. An integration
length of 30 samples is used for smoke measurements.
[0678] To perform the background cancellation techniques, the
receiver also needs to capture images just before and just after
the flash that are used to eliminate the contribution from the
scene. Ideally these "off" exposures would occur as close to the
"on" exposure as possible to optimise cancellation in the case of a
time varying background. With the receiver system used in the
preferred implementation, the maximum practical frame rate is 1000
fps, so the "off" exposures are spaced 1 ms either side of the "on"
exposure.
[0679] In one form, the transmitter optical output consists of a
series of short pulses, with a very low duty cycle. The pulses are
placed to match the frame rate of the imaging system (e.g. 1000
fps). FIG. 92 shows an exemplary pulse sequence in relation to the
sensor exposures in the receiver. In this case the transmitter is
adapted to emit light in an IR wavelength band and an .mu.v
wavelength band. This series of pulses is repeated with a period of
9000 ms.
[0680] In the example, there are 5 pulses, as follows: [0681] Sync
1 (frame 1) 110 and Sync 2 (frame 2) 112: .Sync pulses are used to
maintain synchronisation (discussed more fully later) between the
transmitter and receiver. These are pulses are preferably made in
the wavelength band which is most power efficient. In this case the
IR light source is used because it results in lower power
consumption. Moreover the longer wavelength is more able to
penetrate smoke, so synchronisation can be maintained in a greater
range of conditions. The Sync pulses are 50 .mu.s long. [0682]
Ideally each synch pulse is centred in time on the leading (sync 1)
and trailing edges (sync 2) of the receiver's shutter open period.
This makes their received intensity vary with small synchronisation
errors. [0683] IR (frame 5) 114 and UV (frame 7) 116. The IR and UV
pulses are used for signal level measurement (and in turn used to
measure attenuation and smoke level.). They are 50 .mu.s long,
which allows for up to 25 .mu.s timing error between transmitter
and receiver without influencing the received intensity. [0684]
Data (frame 9) 118: The data pulse is used to transfer a small
amount of data to the receiver. The data is encoded by a either
transmitting or not transmitting the data pulse. The data pulse has
reduced amplitude to save power, and is IR for the same reason.
They are 50 .mu.s long. This system provides a 3 bps data channel.
The data may include serial number, date of manufacture, total
running time, battery status and fault conditions. Those skilled in
the art would be aware of many alternative ways to send data in
this system. These could include pulse position encoding, pulse
width encoding, and multi level encoding schemes. Greater data
rates could readily be achieved, however the simple scheme used in
the preferred implementation is sufficient for the small amount of
data needed.
[0685] In FIG. 92, the data from the receiver during "off" frames
(i.e. frames with no corresponding transmitter output) are used for
the following purposes: [0686] Frame 0 & 3 are used for
background cancellation of the sync pulses [0687] Frame 4 & 6
are used for background cancellation of the IR pulse [0688] Frame 6
& 8 are used for background cancellation of the UV pulse [0689]
Frame 8 & 10 are used for background cancellation of the Data
pulse [0690] (a) Spatial Search
[0691] As described above, the receiver receives each of the
transmitted pulses in the form of one or more pixels within an
image frame.
[0692] However, during commissioning when the system commences
operation (at least the first time) the locations of the
transmitter(s) within the image frame must be established. This
could be performed for example, by a manual process involving an
operator inspecting the image, and programming in the co-ordinates.
However, the need for special training, special tools, and long
complex installation processes for installation is undesirable. In
the preferred embodiment determining the location of the
transmitters within the image frame is automated. The preformed
process for locating transmitters operates as follows: [0693] The
system first captures a number of images at a high frame rate and
for a time sufficient to ensure that transmitter pulses, if the
transmitter is within the field of view of the camera and pulses
are transmitted during the period of capture, will be present in
one or more images. [0694] The system then subtracts each pair of
(temporally) adjacent images, and takes the modulus of each pixel
and then tests each against a threshold to detect locations of
large variation, at which a transmitter may be present. [0695] The
system then condenses the candidate list of transmitter locations
by merging candidate points that are adjacent or nearby. (e.g.
<3 pixels apart) A centre of gravity method can be used to find
the centre of a set of candidate points. [0696] The system then
performs a trial synchronisation (using the process described
below) at each of the candidate centres to verify that the received
value at a candidate centre corresponds to a real transmitter.
[0697] The system then checks that the number of transmitters
matches the expected number of transmitters. This number may be set
by pre-programming the receiver prior to installation, or by a
switch or switches mounted on, in, or connected to the receiver
unit. In the preferred implementation, there is a set of
configuration DIP Switches incorporated into the receiver unit and
easily accessible only while the system is not mounted to the
wall.
[0698] The set of transmitter locations within the image is stored
in non-volatile memory. The locations can be cleared by placing the
receiver into a particular mode, e.g. by setting the DIP switches
to a particular setting and powering/de-powering the receiver, or
by the use of a special tool, such as a notebook PC. This is only
required if a transmitter is moved from its original location or
the system is to be re-installed elsewhere.
[0699] Performance limitations in the imaging system may limit the
number of pixels or lines that can be read out when operating at a
high frame rate. In one implementation, a maximum of 30 lines of
640 pixels can be read out in 1 ms. Therefore the first few steps
of the above method need to be repeated 16 times to cover the
entire 640*480 image frame. Alternatively, some embodiments employ
only part of the image frame. Similarly, some embodiments use a
slower frame rate. However, the possibility of sensor saturation in
bright lighting conditions generally limits exposure time, and
variations in background lighting conditions generally introduce
more noise if a lower frame rate is used.
[0700] The frame rate must be chosen to ensure that the transmitter
pulses do not always occur in period where the shutter is closed.
For example, if the frame rate is exactly 1000 fps, with an
exposure of 100 us, and the transmitter produces pulses on exact 1
ms boundaries, the pulses may all be generated at times when the
shutter is closed. The receiver frame rate is chosen so that there
is a slight difference causing a gradual phase shift, ensuring that
sooner or later the pulses will fall sufficiently within a shutter
open period.
[0701] In some embodiments, processing speed limitations are
managed by not analysing all of the pixels, instead only every nth
(eg. 4th) horizontal and vertical pixel are subtracted and checked,
reducing processing effort (eg. by a factor of 16). Provided that
the received image i.e. the image of each transmitter on the
sensor, is spread over a sufficiently larger area (e.g. a spot
having a diameter of 5 pixels), then the transmitter will still be
found reliably.
[0702] Whenever the system is powered up, either with a known set
of transmitter locations or as a part of the Spatial Search
described above, with a set of candidate locations, a phase search
and lock method is used to establish initial synchronisation.
[0703] The major steps of this method are:
[0704] The system captures images at a high frame rate (at least a
partial image in the expected location).
[0705] The system waits for the expected pattern of pulses to
appear at the candidate centre locations.
[0706] The system uses the time of arrival of a selected pulse
within the expected pattern as a starting phase for the phase
locked loop.
[0707] The system waits for stabilisation of the PLL. If no PLL
lock is made, then in the case of testing candidate locations, the
location is marked as spurious, otherwise when re-establishing
synchronisation with a known transmitter location the receiver can
re-try continually and assert a fault until it is successful.
[0708] As with the spatial search, a small offset in the receiver
frame rate is used to cause a gradual phase shift, ensuring that
sooner or later the pulses will fall sufficiently within a shutter
open period.
[0709] For each frame, the total intensity is calculated within a
small region of the image centred on the known or candidate
location. This sequence of intensity values is then checked for the
expected pattern from the transmitter.
[0710] The test for the expected pattern operates as follows:
[0711] After at least 9 frame intensity values have been collected,
they can be tested for the presence of the expected transmitter
pulse sequence in the following manner.
[0712] Given the intensity values I(n), 0<n<N,
[0713] Test for a possible transmitter signal starting with its
frame 0 at frame n received
[0714] First, compute an "off frame" reference level
I.sub.0=(I.sub.R(n+0)+I.sub.R(n+3)+I.sub.R(n+4)+I.sub.R(n+6)+I.sub.R(n+8-
))/5{ mean of "off frames"}
[0715] Compute relative intensities
I.sub.R(n+m)=I(n+m)-I.sub.0 for m=0 to 8
[0716] Compare with pre-determined thresholds to determine the
presence or absence of a transmitter pulse in each frame
Found = { ( I R ( n + 1 ) > I ON ) or ( I R ( n + 2 ) > I ON
) } and { Sync 1 or Sync 2 pulse } ##EQU00001## ( I R ( n + 5 )
> I ON ) and { IR pulse } ##EQU00001.2## ( I R ( n + 7 ) > I
ON ) and { UV pulse } ##EQU00001.3## ( I R ( n + 0 ) < I OFF )
and { off frame } ##EQU00001.4## ( I R ( n + 3 ) < I OFF ) and {
off frame } ##EQU00001.5## ( I R ( n + 4 ) < I OFF ) and { off
frame } ##EQU00001.6## ( I R ( n + 6 ) < I OFF ) and { off frame
} ##EQU00001.7## ( I R ( n + 8 ) < I OFF ) and { off frame }
##EQU00001.8##
[0717] Due to the random phase errors, either of the sync pulses
may be completely missing, hence the "or" in the above expression.
Alternatively, the tests for the sync pulses can be omitted
entirely, and the tests for the off frames can also be reduced.
However, care must be taken to ensure that the position of the
transmitter pulse sequence is not falsely identified.
[0718] Following a positive detection, the time corresponding to
the frame n is recorded in a variable. The amplitudes of the phase
pulses can be used to trim the recorded time value to more closely
represent the start of the sequence. This helps reduce the initial
phase error that the phased locked loop has to deal with, and may
not be required if frequency errors are sufficiently small.
[0719] In the preferred implementation the image capture rate 1000
fps which matches the transmitter timing as previously described. A
shutter time of 100 .mu.s is used.
[0720] This completes the initial synchronisation. The arrival time
of the next set of pulses can now be predicted by simply adding the
known transmitter period to the time recorded in the previous
step.
[0721] Although the transmitter period is known to the receiver
(300 ms in the preferred implementation), there will be small
errors in the clock frequencies at each end. This will inevitably
cause the transmitted pulses to become misaligned with the receiver
shutter open time. A Phase Locked Loop system is used to maintain
the correct phase or timing. The PLL concept is well known so will
not be described in detail. In the preferred implementation the PLL
control equations are implemented in software. The Phase Comparator
function is based on measuring the amplitude of the phase pulses.
These amplitude are calculated by subtracting the mean of the
intensities measured in the nearest off frames (frames 0 & 3).
The phase error is then computed with the following formula:
= I R ( 1 ) - I R ( 2 ) 2 ( I R ( 1 ) + I R ( 2 ) ) T
##EQU00002##
where T is the width of the phase pulses.
[0722] In the case that the phase pulse amplitudes fall below a
pre-determined threshold, the phase error is assigned a value of
zero. This way noisy data is permitted into the PLL, and in
practice the system is able to maintain adequate synchronisation
for at least a few minutes. Therefore, high smoke levels do not
cause a synchronisation failure before an alarm can be signalled.
In the case of an obstruction, this feature allows the system to
recover rapidly when the blockage is removed.
[0723] The PLL control equations include proportional and integral
terms. It was not found necessary to use a differential term. In
the preferred implementation proportional gain and integrator gains
of 0.3 and 0.01 respectively were found to produce acceptable
results. In a further variation, the gains can be set to larger
values initially, and reduced after the phase error is below a
pre-determined threshold, thus reducing overall lock time for a
given loop bandwidth.
[0724] Phase error below +/-10 .mu.s can be used to indicate phase
lock, both for the purpose of verifying a candidate transmitter
location and also for allowing normal smoke detection operation to
commence.
[0725] FIG. 93 illustrates an environmental monitoring system 9300
adapted to monitor a region 9302 within a room 9304. The
environmental monitoring system includes a beam detection subsystem
9306 which includes a receiver 9308 and four transmitters 9310,
9312, 9314, 9316. The beam detection subsystem operates in
accordance with an embodiment of any one of the systems described
above.
[0726] The environmental monitoring system 9300 additionally
includes four additional environmental monitors 9318, 9320, 9322,
9324. Each of the additional environmental monitors 9318 to 9324
may be of the same type but alternatively each may be of a
different type i.e. sense a different environmental condition or
the same condition by a different mechanism. The environmental
monitors can include, for example, carbon dioxide, carbon monoxide,
temperature, flame, other gas sensors or the like. Each of the
additional environmental monitors 9318 to 9324 is connected by a
communications channel to a nearby transmitter of the beam
detection subsystem. For example, the additional environmental
monitor 9318 is connected via wire 9326 to corresponding
transmitter 9310 of the beam detection subsystem 9306. Similarly,
environmental monitor 9320 is in data communication with
transmitter 9312, environmental monitor 9322 is data communication
with transmitter 9314 and the environmental monitor 9324 is in data
communication with transmitter 9316. The data communications
channel between each environmental monitor and its respective
transmitter may be hard wired connection or may be via a wireless
connection e.g. radio, optical etc. communications link. In most
embodiments the communications link need only be unidirectional,
however it may in some embodiments be bidirectional. In the
unidirectional case, the communications channel is adapted such
that the environmental monitor can communicate an alarm and/or
fault condition detected by it, or other output, e.g. a raw or
processed sensor output to the transmitter of the beam detection
subsystem 9606.
[0727] As will be appreciated the environmental sensors can be
housed within the transmitters rather than located remotely and
connected by a long wire or communications link.
[0728] The transmitter of the beam detection subsystem 9306 is
adapted to receive signals from the environmental monitor and
re-transmit these, with or without additional encoding, via an
optical communications channel, back to the receiver 9308. The
optical communications channel may be implemented by modulating
either the particle detection beam or a secondary beam transmitted
by the transmitter to the receiver 9308. The communications channel
can be alternately or intermittently transmitted between pulses of
the particle detection beam generated by the transmitter.
Alternatively, it may be continuously illuminated, possibly
simultaneously with a particle detection beam. In this case, the
wavelength used for the particle detection beam or beams can be
different to that on which the optical communications channel is
implemented.
[0729] Using such a system, a network of environmental monitors may
be placed around the region being monitored 9302, and the
environmental conditions sensed by these monitors can be
communicated back to the receiver of the beam detection subsystem.
The receiver 9308 is in data communication with a fire alarm
control panel e.g. via a fire alarm loop or proprietary network or
other notification system without the need for complicated
dedicated wiring system between the environmental monitor network
and the fire alarm system. In a preferred embodiment, a plurality
of optical communications channels can be differently encoded such
that a receiver of the beam detection subsystem can distinguish
each optical communications channel from each other. For example,
each optical communications channel may be modulated differently or
may be scheduled to operate in a different time period. Thus
effectively a time division multiplexing arrangement can be
implemented for the different optical communications channels.
Using different wavelengths for each communications channel may
also be possible.
[0730] The system also enables the location at which an
environmental condition is detected to be determined since the
receiver 9308 can resolve optical channels from the different
transmitters e.g. based on the signal received or where on the
sensor the signal arrives if the receivers sensor is of a
multi-sensor element type. The addressing information or channel
information can be passed to the fire alarm control panel and the
location of the alert be passed to an operator or fire
authority.
[0731] In the example of FIG. 93 each of the transmitters and
environmental monitors are preferably battery powered to remove any
need for wiring.
[0732] FIG. 94 illustrates a further embodiment of this aspect of
the present invention. In this embodiment, the environmental
monitoring system 9400 includes a beam detection subsystem 9402 as
well as an environmental monitoring subsystem 9404. The beam
detection subsystem includes a receiver 9406 and a transmitter
9408. The transmitter is adapted to emit one or more beams of light
9410 which are received by the receiver 9406. The receiver 9406 has
a wide field of view having edges indicated by lines 9409, 9409B.
Within the field of view of the receiver 9406 there are positioned
two environmental monitors 9412, 9414. Environmental monitors 9412
and 9414 may be of any of the types described above, and
additionally include a respective light emitter 9416, 9418. The
light emitters 9416, 9418 may be a low power LED or the like and
are used to generate an optical signal which is received by the
receiver 9406. Each of the LEDs 9416, 9418 can be individually
modulated to communicate an output of the corresponding
environmental monitors 9412, 9414 back to the receiver 9406. As
described in the previous embodiment, the optical communications
channels can be either time multiplexed or wavelength multiplexed
with each other and with the particle detection beam or beams 9410
emitted by the transmitter 9408. This embodiment has the additional
advantage over that of FIG. 93 that there is no need for any wiring
or communications channel between the environmental monitors 9412
and 9414 and the particle detection subsystem transmitter 9408.
Accordingly installation costs are minimised.
[0733] FIG. 95 illustrates a component of a particle detector
system. The component 9500 is a light source which is used to emit
one or more beams of light across a volume being monitored for
particles. The light source 9500 includes one or more light
emitters 9502 which are connected to circuitry 9504 which deliver
power to the light emitters 9502. The operation of the light
emitter 9502 is controlled by a microcontroller 9506 which causes
the light emitters to be illuminated in a predetermined fashion,
e.g. to flash in a particular sequence. The light source 9500 is
powered by a battery 9508. The output of the battery is monitored
by monitoring component 9510 and the environmental conditions in
which the component is operating are monitored by the environmental
monitor 9512. The environmental monitor 9512 can be a temperature
sensing device such as a thermocouple. The controller 9506 receives
the output of the battery monitor 9510 and the output of the
environmental sensor 9512 and determines an expected battery
life.
[0734] More particularly, the controller receives signal
representing the temperature of the immediate surroundings of the
battery and the measured output voltage of the battery 9508. The
battery output voltage is compared to a threshold voltage
corresponding to the measured temperature and the discharge state
of the battery 9508 is determined.
[0735] In an alternative embodiment, the battery monitor 9510 is
adapted to measure the total current drawn from the battery. For
example, the monitor 9510 can be an ammeter and determine the level
of current being drawn from the battery. In this case, the
controller is adapted to integrate the measured current over time
and the remaining available charge is determined. When the
remaining charge available is calculated to fall below the
predetermined threshold an indication can be generated of the
impending discharged state of the battery.
[0736] In a further alternative, an estimate of the total current
used can be made. For example, in a preferred embodiment the
majority of the charge drawn from the battery will be drawn in
pulses which are used for flashing the light emitters 9502. If the
circuitry 9504 operates at a constant current, which is preferred,
the duration of operation of the LED multiplied by this constant
current will provide a relatively accurate measurement of the total
charge used by the system over time. In a cruder alternative the
typical average current consumption known to be required by the
equipment can be pre-calculated and the length of time of operation
of the component can be used to determine the total current drawn
from the battery over time.
[0737] In the above embodiments, the environmental conditions, most
advantageously the temperature of the immediate surroundings of the
battery can be monitored over time and this temperature data can be
used by the controller to produce a more accurate estimate of the
remaining charge available in the battery 9808. As will be
appreciated the controller can be adapted to calculate an estimate
of the remaining battery life available under the prevailing
conditions. The remaining time can be compared to a warning
threshold and if the threshold is exceeded an indication of an
approaching discharged state can be generated.
[0738] In a preferred embodiment the predetermined time threshold
at which an indication of an approaching discharged state of the
battery will be generated, may be selected in order to allow
maintenance personnel to receive an indication of the impending
discharge of the battery during a scheduled maintenance event. If
the warning of the impending discharge of the battery can be given
at a sufficiently early stage, say before the scheduled maintenance
event prior to another scheduled maintenance event at which the
battery will need to be changed then no extra unscheduled
maintenance event will be required. Moreover, the maintenance
personnel can ensure that the required equipment e.g. specialised
tools and a battery is obtained prior to the maintenance event at
which the battery will need to be changed. For example, where a
component has a nominal battery life of 5 years and an annual
maintenance inspection is scheduled, an indication of impending
battery failure can be raised say 13 or 14 months before the
nominal end of life. In this way at the inspection arising about 4
years after commissioning of the system the maintenance personnel
will detect that the battery will need to be changed at the
following maintenance session (in a year's time) and can plan to
bring a replacement battery on the next annual visit. It should be
understood that to avoid failure of the system the nominal battery
life is set with a significant safety margin. The time of 13 or 14
months is chosen to allow a scheduling margin for the two
maintenance sessions i.e. the one at which the maintenance
personnel learns of the battery discharge state, and the next one
at which it will be changed.
[0739] In a preferred form of the present invention, when the
component being monitored is a light source of the particle
detector, the light source controller can be adapted to signal the
battery state to the receiver. This can be done by modulating the
amplitude, duration and/or timing of one or more transmitted light
pulses in a predetermined fashion. The light pulse used for data
transmission can be one of the light pulses used in particle
detection or an additional light pulse added to the sequence of
light pulses produced by the light source for the purposes of data
communication from the light source to the receiver. As described
above, such a scheme avoids the need for wiring between the units.
Alternatively, the light source may be fitted with additional low
powered LED which can be flashed to indicate to a person (rather
than the receiver) located remotely from it, the state of its
battery.
[0740] In a particularly sophisticated embodiment, the controller
of the light source can be adapted to generate a battery output
signal e.g. by modulating a light beam in a particular code, with
which indicates a time until expected a battery discharge. For
example, the output signal can indicate the number of months until
the battery is expected to be flat. This allows the maintenance
personnel to more accurately schedule the next scheduled
maintenance session, and also determine if the battery will need to
be replaced before the next scheduled visit. Moreover if an
accurate `time to full discharge` is known then the light source
can go into a low power mode e.g. in which its duty cycle is
reduced from normal to extend battery life. The receiver can be
programmed to detect this low duty cycle mode and indicate a fault
if a low duty cycle modulation patterns is observed.
[0741] FIG. 96 illustrates a system according to a further
embodiment of the present invention. In this system 9600 there is
provided a first receiver 9602 which is associated with a pair of
transmitters 9604 and 9608. The first transmitter 9604 transmits a
first beam of light 9606, and the second transmitter 9608 transmits
corresponding beam of light 9610. Both beams of light are received
by the receiver 9602 and particle detection decisions can be made
in accordance with embodiments of the invention described herein.
The system 9600 additionally includes a receiver 9612 and
associated transmitter 9614 which transmits a beam of light 9616.
The beam 9616 is received by the receiver 9612 which can be adapted
to determine the presence of particles as described elsewhere
herein. The beam detector arrangement effectively provides three
beam detectors that have beams that are coincident (or practically
coincident) at two places. Both of the receivers 9602 and 9612 are
connected to a controller 9618 which is adapted to apply fault
and/or alarm logic to determine that the fault conditions and/or
particle detection conditions exist. As will be appreciated, the
intersecting beams 9606 and 9616, and 9610 and 9616 enable the
system 9600 to determine whether particles have been detected at
the points of intersection of the beams by correlations the outputs
from the receivers 9602 and 9612. Such an arrangement also enables
relatively advanced processing to be implemented and enables the
particle detection algorithms of each of the individual beam
detectors to differ from that used in a single stand alone beam
detector. For example, a simple double knock system can be
implemented in which at least two of the beams must detect
particles above a predetermined threshold level before an alarm is
raised. In a preferred form such a system may reduce overall false
alarm rates as a false alarm condition is unlikely to occur in two
different beams. However, this also permits a lower alarm threshold
to be used, thus enabling faster detection of particles, without
substantially affecting the false alarm rate of the system. In such
a system, the false alarm probability of the entire system is the
same as the product of the individual false alarm probabilities of
the beams. As will be appreciated, both of the advantages of the
above systems can be obtained to some extent by setting an alarm
threshold which compromises between sensitivity and false alarm
rate improvement. Moreover, temporal characteristics of the
particle detection outputs of the various beam detectors can be
used to improve particle detection performance or reduce false
alarm occurrences. In this regard, the time separation between
occurrences of suspected smoke events in each of the beams can be
used to improve probability of early detection without increasing
false alarm. For example, the time which each of a pair of
substantially coincident beams goes into alarm, can be used to
determine whether the alarm condition is caused by the presence of
particles or a false alarm. If they are substantially coincident in
time then the particle detection event is likely to be genuine. On
the other hand, if the particle detection event occurs at
substantially different times in each of the beams then this is
likely to indicate a false alarm is present. In sophisticated
systems it may be possible to compare time varying particle
detection profiles from each of the beam detectors to identify
corresponding particle detection events. For example, this could be
done by cross correlating the outputs of a plurality of
substantially coincident beam detectors within the system. In the
event that high cross correlation between a pair of outputs is
determined this can indicate that the output of each of the beam
detectors are both experiencing similar conditions e.g. the same
particle detection event or same false alarm event. A determination
as to which type of event it is could be made by analysing the
profiles e.g. a duration of obscuration; a level of obscuration;
rate of change at the outset of observation etc to determine if the
event is caused by the presence of particles or a foreign body.
[0742] It will be understood that the invention disclosed and
defined in this specification extends to all alternative
combinations of two or more of the individual features mentioned or
evident from the text or drawings. All of these different
combinations constitute various alternative aspects of the
invention.
* * * * *